Onions are a major provider of essential nutrients and bioactive compounds.  Sulphides in onions acts as a sulphur donor that assists with detoxification, protein synthesis and the building of cell structures.  Onions also contain fibre, potassium, iron, calcium and folic acid.  Onions are healthy whether they are eaten raw or uncooked, though raw onions will provide higher levels of sulphur compounds.  A study by the Journal of Agricultural and Food Chemistry found there were higher concentrations of flavonoids in the outer layers of onion flesh.  Onions (Allium cepa L.) are also an excellent sources of vitamin C, sulphuric compounds and phytonutrients.


Vitamin C is an antioxidant that is essential for the maintenance of connective tissue that houses the hair follicle and protein metabolism that is responsible for the hair fibre.

Flavonoids are responsible for the pigments in many fruits and vegetables and are known to possess hair growth promoting properties [1].  Two flavonoid sub groups can be found in onions, the anthocyanins, which impart the purple/ red colour to red onions and flavanols such as quercetin, these act as antioxidants and provides certain hair health benefits.

The sulphuric compounds in onions are disulphides, trisulphides (collectively known as cysteine sulphoxides), these sulphides can react with components of the scalp such as the proteoglycans and glycosaminoglycans that contribute to the regulation and growth of the hair follicle [2].


  1. Digestion of fat-soluble vitamins | The sulphur content in onion contributes to bile production and the uptake of fat-soluble vitamins.  Fat soluble vitamins like vitamin A, vitamin Dvitamin E and vitamin K are integral to hair follicle health.
  2. Anti-inflammatory | Sulphur compounds have anti-inflammatory and antioxidant properties.  The polyphenols in onions act as antioxidants against free radicals.  Antioxidants increase the growth and repair capacity of keratin cells and increases glutathione, the cells major reservoir of cysteine.  Cysteine and methionine are the only sulphur donating amino acids and low levels of cysteine reduces the density of the hair fibre and the capacity of the hair cycle for growth.  Once the cysteine reservoir in the cell is depleted, the cell will struggle to produce keratin protein, the major building blocks of the hair.
  3. Gut health | Onions contain oligofructose, a type of prebiotic fibre that feeds the ‘good bacteria’ our gut.  The consumption of prebiotic fibres will increase levels of Bifidobacterium and Lactobacillus in the gut.  The correct balance of gut bacteria is needed for a healthy immune system.
  4. Regulation of blood sugar | The chromium in onions assist in regulating blood sugar.  A study in 2014 in the Journal Nutrition found that patients with Type II diabetes saw lower blood sugar levels and normalised liver enzymes when consuming raw sliced onions [3].  The hair follicle is subject to oxidative damage when blood sugar levels are high.  When there are high levels of circulating insulin in response to high blood sugar, blood vessels narrow and blood flow to the scalp is reduced.


Eating raw onions can cause minor side effects for some individuals.  Raw onions can increase the severity of heartburn in those with chronic heartburn and gastric reflux disease.  It is also possible to have a specific allergic reaction or a food intolerance to onions, though this is rare.  People with onion allergies can experience rashes or itchy eyes.  An intolerance to onions may result in vomiting, nausea and other gastric issues.


There is no definitive number of onions you should eat per day, but it may be wise to add a raw onion salad to your diet once or twice a week.  Mix your onion salad with meat, fish or veg for a complete meal and consider adding yoghurt and other condiments.

Nutrition facts (1 medium onion / 143 grams), total carbohydrate 11 grams (4% DV), dietary fibre 3 grams (12% DV), potassium 190 milligrams (5%), protein 1 gram; vitamin C (20% DV), calcium (4%DV), iron (4%DV).

*DV = Daily value based on 2000 calories

Red onion Indian salad – Slice 4 red onions thinly and mix with 4 tablespoons of Greek yoghurt.  Add 1 teaspoon of chilli powder, 2 teaspoons curry powder.  Add 1 teaspoon of salt and one teaspoon of pepper.  Add 6 teaspoons each of chopped mint and coriander.  Add 6 teaspoons of lime juice, 6 teaspoons of rice vinegar.  Mix until combined.

Red onion Turkish sumac salad – Slice 4 red onions thinly and mix with 1 teaspoon of sumac, 1 teaspoon salt.  Add 1 teaspoon red pepper flakes and a half a cup of parsley.  Add 2 tablespoons of lemon juice and 4 tablespoons of olive oil.

White onion and cucumber salad – Slice 1 onion thinly and 3 cucumbers.   Mix with half a cup of apple cider vinegar and 4 tablespoons of olive oil and 4 tablespoons of water.  Add 2 tablespoons of dill and salt and pepper to taste.


Onions are healthy whether they are raw or cooked, though raw onions are a fantastic source of compounds that are great for hair health.  Whilst some experts swear by the benefits of applying onion juice directly to the scalp, incorporating into the diet avoids the sulphurous onion aroma staying with you all day.


  1. Hair growth promoting effect of Dicerocaryum senecioides phytochemicals. International journal of medicinal chemistry, 2019.
  2. Onions—a global benefit to health. Phytotherapy research, 16(7), pp.603-615.
  3. Spice plant Allium cepa: Dietary supplement for treatment of type 2 diabetes mellitus. Nutrition, 30(10), pp.1128-1137.