Onions (Allium cepa) are one of the most popular root vegetables. They’re commonly used in cooking to add flavor or in traditional medicine to treat symptoms of ailments such as the common flu (1, 2).

They are a great addition to your diet. Their sulfur-containing compounds and antioxidants, such as quercetin, have been found to give onions therapeutic potential to reduce inflammation, lower blood pressure, and support blood sugar control (2, 3, 4).

However, there are several myths about the best ways and times to consume onions to gain their health benefits, and you may feel confused or overwhelmed by all the conflicting opinions.

In this article, we dispel popular onion myths, discuss how to handle onion breath, and recommend who should avoid eating onions.

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There are plenty of myths about onions, especially surrounding the best time to eat them.

Myth: It’s best to eat onions at night

Fact: Sulfoxides in onions may support sleep, but onions can be enjoyed at any time of day.

Sulfoxides are the sulfur-containing compounds found in onions that confer some of their health benefits, such as potential anticlotting, antibiotic, and anti-asthma properties (5, 6).

These sulfoxides are activated when onions are cut or crushed. They have been shown to improve sleep quality in healthy adults when taken as a concentrated supplement extract (6).

Therefore, it is believed that you will sleep better if you eat onions at night.

However, the sulfoxides found naturally in raw onions are in much lower concentrations than those found in onion extract powders and supplements. It’s unclear whether the low concentration in raw onion improves sleep.

Furthermore, there’s no research demonstrating a benefit of eating onion at night as compared with any other time of the day.

Myth: Eat onions just before sexual activity

Fact: Onions increase testosterone levels in males but may not enhance your sexual experience.

Onions are lauded as aphrodisiacs — foods that stimulate sexual desire — and have been shown to enhance testosterone production in males (7).

Older studies also show that fresh onion juice increases testosterone and ejaculation in male rats (8).

Therefore, eating onions may improve male sexual health by promoting testosterone production. Testosterone is the reproductive hormone responsible for libido, potency, and even energy levels in males (9, 10).

Despite these findings, however, eating onions has not been found to enhance sexual experience directly.

There’s also no current research that indicates eating onions boosts reproductive hormones in females.


Sulfoxides in onions may support sleep, but you can enjoy onions at any time of the day, not just at night. Onions also improve testosterone production in males but are not likely to enhance your sexual experience.

Red, white, and yellow onions are low calorie foods that provide small amounts of essential minerals like calcium and magnesium (11).

They are one of the richest sources of the polyphenol quercetin, a health-promoting compound with antioxidant and anti-inflammatory properties (2, 3, 4).

Sulfoxides in onions may also reduce depression and stress and help improve sleep. Therefore, incorporating onions as part of a balanced diet could offer many health benefits (5, 6).

Typically, cooking vegetables reduces their nutrient content. For this reason, many people recommend consuming vegetables raw or cooking them for only short periods (12).

However, the effect of cooking on vegetables’ nutrient composition is not a true binary.

For example, research on yellow and red onions has shown that cooking — especially baking — increases the availability of health-promoting polyphenols in the onions (13).

According to one research review, baking, sauteing, and microwaving are the most beneficial cooking methods to maintain or increase the content of health-promoting compounds in onions (14).

That means eating raw onions is not necessarily superior to eating them after they’ve been cooked — you may actually benefit more from eating cooked onions.


Cooking enhances the health-promoting polyphenol content of onions. Therefore, cooked onions may offer more health benefits than raw onions when eaten as part of a balanced diet.

Despite the potential health benefits of onions, not everyone should consume them regularly.

Cooked onions have been shown to induce an allergic reaction in some people by inflaming the skin, which is called dermatitis, or by triggering an asthmatic event. Onion is also an allergenic food in people with sulfur allergies (15).

Onions contain poorly absorbed compounds called fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs), which may trigger abdominal discomfort and bowel irregularities in people with irritable bowel syndrome (IBS) (16, 17).

Therefore, you may want to limit or avoid onions in your diet if you have a sulfur allergy, are allergic to onions, or live with IBS.

Read more about potential downsides of onions here.


People who have an allergy to sulfur or to onions themselves or who have IBS may benefit from limiting or avoiding onions in their diets.

You can thank the health-promoting sulfoxides in onions for their pungent flavor and aroma (6).

However, onion breath can linger and may seem embarrassing. You can reduce or prevent it with these tips:

  • Cook onions to reduce their pungent aroma.
  • Brush, floss, and use mouthwash immediately after eating onions.
  • Chew peppermint gum after eating onions.
  • Gargle with salt water or a mixture of water and lemon juice.


You can reduce or prevent onion breath by cooking onions, brushing your teeth and using mouthwash immediately after a meal with onions, chewing peppermint gum, or gargling with salt water or water with lemon juice.

Onions are popular vegetables with a multitude of culinary and traditional medicinal uses.

Onions may be enjoyed at any time of day and have not been shown to be beneficial only when consumed at night.

They support improved testosterone production in males but may not directly enhance your sexual experience.

Baking, sauteing, or microwaving onions may offer more benefits than eating them raw, but people with allergies to onions or sulfur, as well as people living with IBS, may benefit from limiting or avoiding onion consumption.

Just one thing

Try this today: You can make baked onion rings at home. Dip 1/2-inch-thick rings of onion into a batter of milk, all-purpose flour, paprika, onion and garlic powders, and salt. Bake at 450°F (230°C) for 15 minutes, until brown, then serve with a meal or as a snack.

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