What Are Hops?
Hops are the female flowers of hop (Humulus lupulus L.), a climbing plant belonging to the same family as hemp (Cannabaceae). Hop most likely originated in China, Southern Caucasus and Siberia, or Mesopotamia, from where it spread to Japan, America, and Central Europe [1, 2].
Due to its role in beer brewing, which accounts for 98% of its use, hop is nowadays cultivated in all warmer regions. The different compounds in hops add a bitter flavor to beer, prevent the growth of unwanted microorganisms during the brewing process, and stabilize foam .
- Lack of appetite
- Digestive issues
- Painful teeth, ears, and nerves
- Kidney stones and urinary inflammation
- Water retention
- Skin ulcers and injuries
- Foot odor
- Blood ‘purification’
However, many of these uses remain scientifically unproven.
- Sleep disturbances
Due to this, research has recently focused on identifying the main biologically active compounds present in hops .
- Melcalin HOPs
The main active components of the hop plant are found in the female flowers. Volatile oils, bitter acids, and prenylflavonoids are produced by hair-shaped glands, while the rest of flavonoid types are most abundant in seeds and specialized leaves [1, 2].
Hops terpenoids are partly responsible for their purported anti-inflammatory, anticancer, antioxidant, and antimicrobial activities .
- α-Acids: The main ones are humulone (35-70% of total α-acids), cohumulone (20-65%), and adhumulone (10-15%).
- β-Acids: Such as lupulone (30-55% of total β-acids), colupulone (40-58%), and adlupulone (6-30%).
Other, less abundant bitter acids include pre- and post- lupulone and humulone. Hops α-acids undergo some chemical reactions that convert them to iso-α-acids .
Hops also contain six different classes of flavonoids :
- Flavan-3-ols: Catechin, gallocatechin
- Proanthocyanidins: Procyanidins B1, B3, and B4, proanthocyanidin C2
- Flavonols: Quercetin, kaempferol, myricetin
- Flavanones: Naringenin
- Flavonol glycosides: Quercetin and kaempferol glycosides
- Prenylflavonoids: Xanthohumol, 8-prenylnaringenin
Although to a lower extent than in hops, active compounds can also be found in other parts of the hop plant such as male flowers (xanthohumol and bitter acids) and leaves (xanthohumol, volatile compounds, and bitter acids) [9, 1].
Health Benefits of Hops
Due to the scarcity of clinical studies, hops and its active components have not been approved by the FDA for medical use. Further research will be required to determine whether they are effective or safe for long-term use.
Nevertheless, hops extract is commercially available as a supplement. Regulations set manufacturing standards for supplements but don’t guarantee that they are safe or effective. Talk to your doctor before using hops supplements to avoid unexpected interactions.
Possibly Effective for:
Menopause is the cessation of menstrual cycles in women. It is accompanied by a reduction in female sex hormone levels, which causes symptoms such as :
- Hot flashes
- Night sweats
- Sleep disturbances
- Mood changes (depression, irritability)
- Bone and muscle mass loss
- Reduced sex drive
- Vaginal dryness
In a pilot trial of 100 women, a gel containing hops extract reduced vaginal dryness .
In several studies in female rats whose ovaries were removed to mimic menopausal hormone deficiency, hops extract or 8-prenylnaringenin reduced hot flashes, improved some bone mass and architecture parameters (although it worsened others), and increased sex drive [14, 15, 16, 17].
In a small trial on 72 menopausal women, a morning/evening formula in which the morning capsule contained ginseng, black cohosh, soy, and green tea extracts and the evening capsule contained black cohosh, soy, kava, hops, and valerian extracts improved several menopausal symptoms including hot flashes and sleep disturbances .
To sum up, hops and its component 8-prenylnaringenin are possibly effective for menopausal complaints based on the existing evidence. Future clinical research should determine the most effective ways to use them therapeutically.
Insufficient Evidence for:
1) Helping Anxiety and Mood Disorders
In a trial on 36 people with at least mild depression, stress, or anxiety, hops extract improved all the symptoms .
In rats, hops extract had antidepressant activity – measured as a reduction of the time that rats spent floating immobile in a cylinder filled with water .
However, a small clinical trial and a study in rats are clearly insufficient to claim that hops help with mood disorders. More clinical studies on larger populations are required.
2) Helping Sleep
In a small trial on 17 people, one can (333 mL, a bit more than 1 cup) of non-alcoholic beer improved sleep quality. Hop was suggested as the main beer component responsible for this effect .
Hops extract increased sleeping time and reduced physical activity and body temperature in mice and rats taking sedatives. In a study in quails, whose sleep-wake rhythm is very similar to that of humans, a dose of 2 mg hops extract was most effective in reducing night activity while preserving a normal circadian activity/rest rhythm [21, 19, 22, 23].
Hops are frequently combined with valerian to fight insomnia. In three trials on over 250 people, this combination was more effective than placebo. Two of them showed that the combination was also more effective than valerian alone [24, 25, 26].
Similarly, the combination of hops, valerian, and purple passionflower was as effective as the drug zolpidem in a trial on 78 people with insomnia .
All in all, the evidence to claim that hops help sleep is promising but insufficient. There are only a few, small clinical trials and animal studies. Additionally, many of the studies used hops in combination with other supplements, making its contribution to the effects observed difficult to estimate.
3) Promoting Weight Loss and Metabolic Health
In a trial on 200 healthy overweight people, hops extract reduced body fat, especially in the belly .
The combination of hops isohumulones and acacia proanthocyanidins improved several symptoms of metabolic syndrome. Together with diet changes and physical exercise, it decreased blood levels of triglycerides and cholesterol (total, LDL, APOB) in a trial on 23 people. The combination also reduced insulin levels while increasing insulin sensitivity in another trial on 91 people [38, 39].
Again, the results are promising but further clinical research is needed to confirm the benefits of hops on weight loss and metabolic health.
4) Supporting Dental Health
Hops polyphenols reduced the capacity of two bacterial species (Streptococcus mutans and Streptococcus sobrinus) to cause cavities .
Two small clinical trials and a few studies in animals and cells cannot be considered sufficient evidence to support this health benefit. More human studies are needed.
5) Helping Fight Allergies
In a clinical trial on 39 people with allergies to pollen, hop extract improved nose swelling, nose color, discharge amount, and discharge characteristics .
In a study in human nose cells, hops water extract reduced the production of a cytokine that activates allergic inflammatory responses (TSLP) .
Once again, very few studies support this health benefit. Further clinical research is needed.
6) Supporting Heart Health
In a small trial on 23 people, hops isohumulones improved blood flow, both in smokers and non-smokers .
In rats, hops extract relaxed blood vessels, which may reduce the risk of heart disease .
Because xanthohumol inhibits platelet activity, it may reduce the risk of blood clot formation (thrombosis) .
Further research in humans is needed to confirm the effects of hops in protecting the heart.
7) Helping Blood Sugar Balance
In a small trial on 20 diabetic people, hops isohumulones reduced blood sugar levels .
In multiple studies with mice and rats, hops extract, its components xanthohumol and isohumulones, or a mixture of hops isohumulones and acacia proanthocyanidins reduced blood sugar levels and insulin resistance [31, 32, 33, 57, 58, 35].
Once again, this health benefit is only supported by one clinical trial and a few animal studies. Further research in humans should confirm these preliminary results.
The simultaneous activation of PPAR-alpha and PPAR-gamma by isohumulones may lower blood sugar levels by reducing insulin resistance. Hops bitter acids also activate the bitter taste receptors and stimulate the production of GLP-1, a protein that triggers insulin production in response to sugar [57, 59].
Xanthohumol may lower blood sugar levels by:
- Binding to the farnesoid X receptor [60, 61]
- Blocking sugar uptake 
- Blocking an enzyme that produces sugar from complex carbohydrates (α-glycosidase) 
While some hops flavonoids (e.g., quercetin) also reduce sugar uptake, others (e.g., catechin) increase it. The hops flavonoids catechin, epicatechin, quercetin, and rutin may also lower blood sugar levels by stimulating the growth of the cells that produce insulin (β-cells) [62, 64+].
8) Using as a Deodorant
In a small trial on 42 people, hops extract mixed with an odor adsorbent agent commonly found in commercial deodorants reduced underarm odor without causing irritation. In the same study, hops extract reduced the growth of two bacterial species responsible for underarm odor (Corynebacterium xerosis and Staphylococcus epidermidis) .
Additional clinical trials should confirm the potential of hops extract as a deodorant.
9) Reducing Pain and Inflammation
A combination of hops isohumulones, rosemary extract, and oleanolic acid reduced the pain caused by arthritis and fibromyalgia in a small trial on 54 people. More studies on larger populations are needed to confirm this potential benefit. Additionally, because the study used a combination of extracts, the specific contribution of hops to the effects observed is not clear .
Animal and Cell Research (Lack of Evidence):
Hops and their compounds are being researched for other potential health benefits. Because the research is still in the animal and cell stage, we cannot draw conclusions.
Preventing Liver Damage
In several mice studies, hops or its components xanthohumol and isohumulones had protective effects against the following liver disorders:
- Alcoholic fatty liver disease [67, 68]
- Non-alcoholic fatty liver disease [69, 70]
- Oxidative damage, inflammation, and cell death associated with aging 
- Tissue scarring in response to liver damage 
Supporting Digestive Function
In a study in pigs, dietary hops (or a grape product also rich in polyphenols) increased weight gain per feed intake. The new diet did not change gut morphology or feed digestibility, but changed the gut microbial composition and reduced the production of pro-inflammatory proteins .
Studies in humans should confirm these preliminary results.
Supporting Skin Health
The intake of hops extract or its components xanthohumol and lupulone reduced skin inflammation (measured as ear swelling) in three studies on mice with mite-induced dermatitis, contact allergic dermatitis, and exposed to a tumor promoter agent [76, 77, 78].
In an antimicrobial study, xanthohumol and lupulones reduced the growth of five microbes that cause acne (Propionibacterium acnes, Staphylococcus epidermidis, Staphylococcus aureus, Kocuria rhizophila, and Staphylococcus pyogenes). Hops compounds also blocked two activities of these bacteria that also contribute to the development of acne (anti-collagenase and oxidative) .
Hops extract reduced brain damage and maintained brain function in rats recovering from a stroke or poisoned with aluminum nitrate. In the long-term, hops extract reduced the buildup of a protein believed to cause Alzheimer’s disease (β-amyloid) in the brain of old mice and preserved their cognitive functions [80, 81, 82].
Because xanthohumol (among other flavonoids) can block an enzyme involved in the onset of Alzheimer’s disease (BACE1), it was suggested as a preventive therapeutic candidate for this disease .
The results of these studies will need to be repeated in larger and more robust studies to confirm a role for hops or its active compounds in preventing neurodegenerative diseases.
Hops essential oil and extracts inhibited [86+]:
- Yersinia enterocolitica
- Salmonella enteritidis
- Salmonella typhimurium
- Proteus mirabilis
- E. coli
- Klebsiella oxytoca
- Mycobacterium fortuitum, a relative of the bacterium that causes tuberculosis .
- Bacteria that may cause diarrhea (Bacteroides fragilis, Clostridium perfringens, Clostridium difficile)
- Antibiotic-resistant strains (Staphylococcus aureus, Enterococcus faecium)
- Bacteria that may cause food poisoning (Staphylococcus aureus and Staphylococcus epidermidis)
- Influenza A virus
- Rhinovirus (the common cold)
- Herpes simplex virus type 1 and 2
Hop’s xanthohumol enhanced the activity of interferon alpha (IFN-α) against a cow virus. Because this virus is very similar to hepatitis C virus, xanthohumol might be used to develop new therapies against it .
Xanthohumol also reduced HIV replication, the production of a virus, and the damage caused to cells. For these reasons, its investigation as a new therapeutic agent for HIV was suggested .
In a study in which five hop components were tested against four human fungal pathogens (Trichophyton mentagrophytes, Trichophyton rubrum, Candida albicans, and Mucor rouxianus), xanthohumol, isoxanthohumol, and 6-isopentenylnaringenin were identified as the most powerful antifungal agents .
It’s important to note that these are very preliminary results that have not yet been studied in humans or even in animals. Further research should determine if hops is effective against infections caused by these organisms when ingested in normal doses.
Preliminary research in animals and cells has found anticancer activity in several of hops’ constituents.
However, many substances – including downright toxic chemicals like bleach – have anti-cancer effects in cells. This doesn’t mean that they have any medical value. On the contrary, most substances (natural or synthetic) that are researched in cancer cells fail to pass further animal studies or clinical trials due to a lack of safety or efficacy.
Do not under any circumstances attempt to replace conventional cancer therapies with hops extract, its components, or any other supplements. If you want to use them as supportive measures, talk to your doctor to avoid any unexpected interactions.
The hops component xanthohumol reduced growth, survival, or migration in cells of the following cancer types:
- Prostate [98, 99, 100, 101]
- Liver [102, 103, 104]
- Pancreatic 
- Stomach 
- Colon [107, 108]
- Breast [109, 110, 111]
- Ovarian [109, 108]
- Cervix [112, 113]
- Lung [114, 112, 108]
- Brain 
- Skin 
- Laryngeal 
- Thyroid 
- Leukemia [118, 119]
Other hops flavonoids such as isoxanthohumol, 6-prenylnaringenin, and 8-prenylnaringenin also showed activity against the following cancer types:
- Prostate [120, 101]
- Kidney 
- Breast [111, 109, 121]
- Colon 
- Ovarian 
- Burkitt lymphoma 
- Skin 
In a study in thyroid-derived cells, xanthohumol improved iodide uptake, which is an essential step in the production of the thyroid hormone. In another study, xanthohumol increased TSH and activity of the enzyme that converts T4 to T3 (type 1 deiodinase) [125, 126].
Limitations and Caveats
Although they have also been tested in animals and cells, only one clinical trial on a small population (17-42 people) supports each of the following health benefits of hops:
- Improvement of mood disorders 
- Sedative 
- Antiallergic 
- Antioxidant 
- Improvement of insulin resistance 
- Deodorant 
The following benefits have only been tested in animal and cell studies:
- Activity against infectious agents [86, 93, 96, 90]
- Anticancer [127, 2]
- Anti-inflammatory [77, 127]
- Protection against brain damage [84, 83, 80]
- Skin health promotion [76, 79]
- Protection against heart disease [52, 53, 55, 56]
- Protection against liver damage [68, 70, 71, 69]
- Improvement of digestive function [73, 75]
- Improvement of thyroid function [125, 126]
Therefore, more clinical trials involving larger amounts of people are required to confirm these claims.
Although doses of up to 239 mg hops extract per day during 7-day periods caused no toxicity symptoms, no long-term toxicity studies have been carried out .
Mechanisms of Action
Several studies have investigated the mechanisms of the main active components of hops extract. Importantly, these studies were done in animals and cells. The effects of these compounds may not be the same in humans.
1) Female Sex Hormone Mechanisms
Some plant substances are called phytoestrogens because they can interact with female sex hormone (estrogen) receptors and trigger some of their responses. The main phytoestrogen found in hops is 8-prenylnaringenin [129, 130].
Female sex hormones are recognized by two kinds of cell receptors :
- ERα: Mostly present in the inner layer of the uterus (endometrium), ovaries, bones, and breast glands
- ERβ: Most common in fatty tissue, the inner lining of blood vessels (endothelium), brain, kidneys, and prostate
Although most phytoestrogens preferentially bind to ERβ, 8-prenylnaringenin binds to ERα. In the tissues where this receptor is found, 8-prenylnaringenin caused the following effects in animal studies [129, 8]:
- Reduced bone mass loss 
- Reduced production of the hormones LH and FSH 
- Increased production of the hormones prolactin and IGF-1 
- Increased breast secretion 
- Increased tissue growth in the vagina and uterus [134, 133]
However, 8-prenylnaringenin can also have anti-female sex hormone effects by blocking aromatase, a key enzyme in estrogen production .
2) Sedative and Anti-Stress Mechanisms
In mice, both α- and β-bitter acids had antidepressant activity and increased the sedative effect of ketamine but they differed in their effect on sleepiness induced by pentobarbital. While α-acids enhanced its effect, β-acids reduced it. Only β-acids reduced the activity of GABA [19, 21, 139].
A fixed valerian-hops combination promoted sleepiness in mice and rats by binding to four different types of receptors:
3) Potential Anticancer Mechanisms
Xanthohumol also killed cancer cells by blocking proteins that promote cell survival, such as:
- Bcl-2 , Survivin 
- mTOR , Akt 
- NF-κB 
- Topoisomerase 
- Aromatase 
- STAT3 
Other mechanisms by which xanthohumol may cause cancer cell death include:
- Increased superoxide production 
- Activation of unfolded protein response 
- Reduced nitric oxide production 
- Reduced production of cytokines (MCP-1 and TNFα ) 
- Activation of programmed cell death [154, 155, 156] and cancer cell autophagy 
- Increased production of proteins that block cell growth and division (p21 and p53) 
Xanthohumol may also prevent the formation of new blood vessels in tumors by blocking growth pathways (NF-κB and Akt) .
Finally, xanthohumol reduces the ability of cancer cells to invade other tissues by:
- Blocking prostaglandin production 
- Reducing the production of a protein that allows cancer cells to migrate outside the tumor (MMP-9) 
- Stimulating an anti-invasive protein complex (E-cadherin/catenin) 
- Reducing the production of chemokine receptors (CXCR4)  and cell attachment proteins (ICAM-1) 
These anticancer effects have been studied in cells and animals at high dosages, but often this doesn’t translate to benefits in humans, especially at normal dosages.
4) Antioxidant Mechanisms
Reactive oxygen species are formed through chemical reactions in the body and cause oxidative damage to DNA, proteins, and fatty molecules. Plant flavonoids prevent the oxidative damage of reactive oxygen species by [165, 166]:
- Breaking them down
- Blocking the enzymes that produce them
- Retaining the minerals required for their production
Xanthohumol and other hops flavonoids activated the following antioxidant proteins:
5) Anti-Inflammatory Mechanisms
Both hops extract and xanthohumol have several proven anti-inflammatory effects, including:
- Reducing T cell growth and killer T cell development 
- Blocking pro-inflammatory proteins (TLR4, NF-κB, CREB, COX1, and COX2) [175, 176, 177, 178]
- Decreasing cytokine (IL-2, IL-6, IL-12, IFN-γ, MCP-1, and TNF-α) and antibody (IgE) production [174, 153, 175, 77, 76]
- Reducing histamine release 
- Blocking nitric oxide production 
6) Fat/Cholesterol-Lowering Mechanisms
Xanthohumol blocks a key enzyme in triglyceride production (diacylglycerol acyltransferase) and the protein that binds newly formed triglycerides to lipoproteins (MTP). This results in a decreased release of the lipoprotein that transports triglycerides through blood (apolipoprotein B) [180, 181, 182, 183].
Xanthohumol also reduces cholesterol buildup inside the arteries by preventing damage to LDL and blocking the protein that transports this fatty molecule from HDL to LDL (cholesteryl ester transfer protein) [184, 185, 186].
Xanthohumol reduces the development and stimulates the death of fatty cells by reducing PPAR-gamma levels, which lowers total body fat accumulation. In turn, isohumulones reduce blood triglyceride levels by activating PPARα. In the liver, xanthohumol prevents triglyceride buildup by binding to the farnesoid X receptor (FXR), which decreases the levels of an enzyme that promotes fat production and fatty cell development (SRBEP1c) [37, 57, 60, 187].
7) Sugar-Lowering Mechanisms
The simultaneous activation of PPAR-alpha and PPAR-gamma by isohumulones lowers blood sugar levels by reducing insulin resistance. Hops bitter acids also activate the bitter taste receptors and stimulate the production of GLP-1, a protein that triggers insulin production in response to sugar [57, 59].
Xanthohumol lowers blood sugar levels by:
- Binding to the farnesoid X receptor [60, 61]
- Blocking sugar uptake 
- Blocking an enzyme that produces sugar from complex carbohydrates (α-glycosidase) 
While some hops flavonoids (e.g., quercetin) also reduce sugar uptake, others (e.g., catechin) increase it. The hops flavonoids catechin, epicatechin, quercetin, and rutin also lower blood sugar levels by stimulating the growth of the cells that produce insulin (β-cells) [62, 64+].
Side Effects & Precautions
Keep in mind that the safety profile of hops and their active compounds is relatively unknown given the scarcity of clinical studies. The list of side effects below is, therefore, not a definite one. You should consult your doctor about other potential side effects based on your health condition and possible drug or supplement interactions.
Although no side effects derived from its use as a medicinal supplement have been reported, hops can trigger allergic reactions in sensitive people, especially in those exposed to high amounts .
- Allergic rhinitis
- Chronic obstructive pulmonary disease
- Bronchial irritation and inflammation
- Dry cough
- Breathing difficulties
- Reduced lung function
- Skin redness
- Fluid buildup in the eyelids
Due to the lack of studies investigating its effects, hops extract should not be used by children younger than 3 years old or women who are pregnant or breastfeeding.
Although some preliminary evidence suggests that 8-prenylnaringenin has anticancer activity, it may stimulate the growth of tumors with female sex hormone receptors (estrogen-positive) and interfere with some breast cancer therapies due to its capacity to bind to estrogen receptors. People with a history of estrogen-positive cancer or receiving breast cancer therapy should contact their doctors before taking hops extract [195, 196, 135, 197].
Hops 8-prenylnaringenin alters the production and effects of female sex hormones, which can lead to fertility problems in premenopausal women. Therefore, young women may want to avoid high dosages of phytoestrogen supplements over extended periods .
The hops compounds xanthohumol and lupulone increased the antibacterial power of the following antibiotics :
In a study in rats, xanthohumol increased the effect of midazolam in reducing anxiety .
In a study in mice, the extracts of two hop varieties (Aroma and Magnum) reduced the hypnotic effect of pentobarbital and diazepam. In both cases, Magnum was the variety with the strongest effect .
In another study, the excitatory effect of cocaine (measured as increased spontaneous movement) was totally blocked by Magnum and partially blocked by wild plant extract. Aroma, Magnum, and wild plant extracts stimulated the pain-relief effect of Tylenol, with Aroma showing a stronger activity than the other two. Hops extract enhanced the effects of Tylenol by slowing down its breakdown in the liver [201, 202].
In the liver and bowel, the enzyme CYP1A2 produces 8-prenylnaringenin from xanthohumol and isoxanthohumol, while CYP2C8 and CYP2C19 convert 8-prenylnaringenin and isoxanthohumol to other compounds with lower female sex hormone activity. Variants of these proteins may increase or reduce the female sex hormone effects of hops .
Variants of PPAR-alpha and PPAR-gamma may have increased or reduced capacity to bind to lupulones. Similarly, farnesoid X receptor versions may have altered capacity to bind to xanthohumol. In both cases, this may alter their effects on blood sugar and fatty molecule levels [57, 60].
Dosage and Toxicity
Because hops extract is approved by the FDA as a food additive but not as a remedy for any conditions, there is no official dose. Supplement manufacturers and users have established unofficial guidelines based on trial and error.
The recommended dose for mood disorders such as anxiety, restlessness, and depression is 200 mg hops extract 2x/day .
Based on their long-term use in brewing and traditional medicine, hops are generally recognized as safe .
A standardized hops extract (21 mg xanthohumol, 1.3 mg 6-prenylnaringenin, 0.8 mg isoxanthohumol, 0.25 mg 8-prenylnaringenin) taken up to 4x/day for one week had no toxicity signs in a study on 5 postmenopausal women .
In rats, a study found no adverse effects derived from up to 4000 mg hops extract/ kg body weight per day. However, high xanthohumol doses (0.5% of diet or 1000 mg/kg body weight) reduced liver weight and breast gland development in another study. Males taking xanthohumol before mating had a higher proportion of male offspring [209, 210].
Dogs that took boiled hops residues experienced a strong malignant reaction characterized by :
- Increased body temperature
- Stomach pain
- Death (in 4 out of 5 cases)
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Most people took hops supplements for insomnia and anxiety. Users were generally happy with the results and reported being able to sleep longer and feeling more relaxed without experiencing side effects such as drowsiness.
Dissatisfied users complained that the supplement had little or no effect. Only one male user reported mild unwanted female sex hormone effects, which he didn’t describe in detail.
Similarly, women taking hops supplements for menopausal symptoms were mostly happy and reported experiencing fewer hot flashes. In some cases, the users complained not feeling any results.
A few users took hops supplements to reduce inflammation and pain. They all reported satisfactory outcomes.