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Onion (Pyaaz): Uses, Benefits, Side Effects and More!

By Dr Siddharth Gupta +2 more


Onion is the most regularly used ingredient in Indian cooking and one of the most widely farmed and consumed vegetables worldwide.1 Allium cepa (commonly known as onion) is a perennial (plant that lives for several years) herb with an underground bulb and a stem. Onions are members of the Liliaceae family. Most commercially grown onions are produced from the plant’s thin, black seeds. Because of their flavour and nutritional benefits, onions are highly valued and stored as pickles.2 Onion is known by many other names, including basal, basl, cebolla, cebolla morada, cepa bulb, cepolla, cipolla, cuhanh, Spanish onion, tamanegi, Madras oignon, oignon, red globe onion, Zwiebel, yellow Bermuda onion, piyaj, piyaz, ralu lunu, sibuyas, loyon, and others.3

Onion grows in both warm and cold climates, in various soil types ranging from dry to moist and mineral-based soils, and is geographically widespread in South West Asia. Shoots, seeds, and bulbs are used to make medicine.3

Onions are the world’s oldest cultivated vegetable. The colour of red onions is mainly attributable to anthocyanins found in the cells of the bulb’s scale leaves. The onion is a multi-use vegetable that is eaten fresh as a salad or used in a variety of processed items. Onions might have various potential health uses in humans.4

Did you know?

  • The sulfur compounds in onions have been found to have anti-inflammatory and anti-cancer properties. source: fdc.nal.usda.gov
  • Consuming onions may help lower blood pressure due to their high potassium content. source: fdc.nal.usda.gov
  • Onions may help improve bone health due to their high content of vitamin C and other nutrients. source: fdc.nal.usda.gov
  • Onions contain compounds that may help reduce the risk of certain types of cancer, such as colorectal and stomach cancer. source: fdc.nal.usda.gov

Nutritional Value of Onion:

The nutritional content of onion is:

NutrientAmount (g/100 g wet weight)
Fat     0.2-0.4
Carbohydrate     5.2-10.5
Energy8 calories
Elementsmg/100 g wet weight
Calcium                                                                   190-540
Phosphorus    200-430
Potassium     80-110
Sodium     31-50
Magnesium      81-150
Aluminium  0.5-1
Barium    0.1-1
Ferric   1.8-2.6
Vitamins                         mg/100 g wet weight
Thiamine        0.3
Vitamin B6      0.1
Nicotinic acid       0.2
Vitamin C      10
Pantothenic acid              0.14
Riboflavin       0.05
Vitamins                          µg/100 g wet weight
Folic acid16

Table1: Nutrients found in onion5

Onion (Pyaaz) bulbs and leaves contain a large number of phytoconstituents such as cyaniding glycosides, prostaglandins, quercetin, sterols, phenol compounds, catechol, protocatechuic acid (in the dried brown outer scale), and diosgenin (in the blossoms and bulbs). Onion oil has a higher concentration of mono, di, tri, tetra-sulphides, thiophene, and thiol compounds. Selenium, quercetin, flavanols, cysteine sulfoxides, flavonoids, allylsulfides, organosulfur compounds, thiosulfinates, cycloallin, fructose, sulphur and seleno compounds, sulfinates, xylose, galactose, glucose, and mannose are also found in onions.3

Also Read: Lady Finger: Uses, Benefits, Side effects and More!

Potential Uses of Onion:

Various properties of onion are listed below.

  • It might help in weight management (anti-obesity activity)1
  • It might help the heart against diseases (heart protective)1
  • It might have an anticancer potential2
  • It might help lower blood sugar (antidiabetic)2
  • It might be an antioxidant2
  • It might have an antiplatelet activity2
  • It might help lower the blood pressure (antihypertensive)2
  • It might have an anti-depression potential
  • It might be helpful for the brain activities (brain protective)
  • It may help relieve the effects of body’s elaborate defensive system (anti-inflammatory activity)2
  • It might have an antiparasitic potential2
  • It might be a bronchodilator (make breathing easier by dilating the bronchi)3
  • It might be an expectorant (cough medicine)3
  • It might have anti-spasmodic (prevents muscle spasms) activity3
  • It might be a carminative (relieves gases from the gastrointestinal tract)3
  • It might act as an anti-coagulant (prevents the clotting of blood)3
  • It might be an anti-helminthic (acts against parasitic worms)3
  • It might help protect the liver (liver protective)3
  • It might have action against bacteria (anti-bacterial)3
  • It might act against viruses (anti-viral)3
  • It might have an anti-pyretic (relieves fever) potential 3
  • It might be an analgesic (pain reliever)3

Though we have tears in our eyes while cutting it in our kitchens, onion is highly nutritious. It is rich in various vitamins like vitamins B1, B6, C, K. It is also rich in biotin and folic acid and minerals like calcium, and flavonoids that act as antioxidants. Additionally, it is also a good source of sulphur which might be beneficial for liver health.

Dr. Siddharth Gupta, B.A.M.S, M.D (Ayu)

Also Read: Karela (Bitter Gourd): Uses, Benefits, Side Effects and More!

Potential Uses of Onion:

1.  Potential uses of onion for cancer:

The potential antioxidant, cytotoxic (toxic to cells), and anti-inflammatory properties of onion peel extract are due to quercetin, which might aid in suppressing the production of reactive oxygen species and might help against oxidative cell damage.1

  According to a study, the potential antiproliferative action of onion peel extract on cancer cell lines (human colon cancer cell line, human osteosarcoma cell line) might be due to a synergistic effect of various bioactive compounds (phytochemicals and flavanols) present in the onion peel.1

Another study found that onion peel extracts might have potential anticancer properties against breast cancer. Cancerous cells exhibit unregulated cell growth as well as abnormalities in apoptotic (cell death) processes. Red onion peel extract might lower cell proliferation and may improve cell cycle arrest in breast cancer cell lines apparently by suppressing a signalling system (which plays a critical role in cell cycle progression) in cancerous cells.1 But, all these claims need to be properly backed-up by clear cut evidence. Furthermore, serious conditions such as cancer must be properly diagnosed and treated by a qualified doctor. Kindly consult a doctor and do not self-medicate.

2.  Potential uses of onion for infections:

Many fungi, bacteria, and viruses have been reported to be affected by onion extracts. According to a study, the essential oils of three onions (red, green, and yellow) have potential antibacterial activity against specific pathogens such as Salmonella enteritidis, Fusarium oxysporum, Penicillium cyclopium, Staphylococcus aureus, and Aspergillus Niger. In studies red onion extract has been demonstrated the potential to have more antibacterial capabilities than yellow and white onion extracts.2

One study found that P. aeruginosa associated with urinary tract infections might be inhibited by onion extract, implying its potentiality for urinary tract infections. Furthermore their essential oils might help limit the growth of dermatophyte fungi (pathogenic fungi that grow on skin, hair, and nails). Onion extract might help reduce the growth of fungi like Fusarium oxysporum and Aspergillus Niger as well.2 Therefore, onion might be effective against various fungal, bacterial and viral infections. Further studies are needed to establish this ability of onion extracts.

3.  Potential uses of onion for obesity:

According to a recent animal study, quercetin from onion peel extracts was found to have potential anti-obesity properties.1 Onion peel extract might help suppress fat accumulation and triglyceride content maybe by inhibiting adipogenesis. One clinical trial investigation on obese healthy women who were administered quercetin rich-onion peel extract capsules might prove to be beneficial for weight management. However, these studies are limited and require wider studies to prove their true impact. Therefore, kindly consult a doctor for healthy weight management methods.

4. Benefits of onion for the brain:

Researchers have studied the brain-protective impact of onion husk extract. It might have a brain-protective effect by helping in raising the brain’s antioxidant levels. Onion solid waste extracts can certain enzymes which might be helpful for Alzheimer’s disease. This extract might also have a memory-enhancing effect   which might be due to its antioxidant effect or due to the inhibition of certain enzymes and pathways.1

Onion might also have an antidepressant potential. Various researchers have observed that the onion bulb might have anxiolytic, antidepressant, and memory-boosting capabilities. These activities need to be proved by more concrete research.

5.  Potential uses of onion for the heart:

According to an animal study, blood lipid and glucose levels reduced dramatically in animals treated with quercetin-rich onion peel extract. There was, however, no effect on cholesterol. Prothrombin time and platelet aggregation were reduced by downregulating several pathways, ultimately reducing thrombosis (blood clotting), indicating that onion peel extract has antithrombotic (prevention of clot formation) effects that might be attributed primarily to quercetin and its derivatives found in onion peel.1

Scientists have discovered that onion peel extract might have the potential to help with hypercholesterolemia (an excess of cholesterol in the bloodstream) in an animal model. Thus, onion peel extract supplementation led to lower blood levels of low-density lipoprotein cholesterol and higher high-density lipoprotein cholesterol, which might ultimately be helpful for heart diseases.1 Kindly consult a doctor for heart diseases. Do not self-medicate.

6. Potential uses of onion for diabetes:                    

According to one study, onion skin extracts might inhibit sucrase, α-glucosidase, maltase, and α-amylase enzymes. In an animal model, onion skin extracts significantly reduced blood glucose levels, implying that quercetin (phenolic phytochemicals) may have a sugar-lowering effect.1

The administration of onion solid waste extracts may enhance insulin sensitivity and might reduce the oxidative stress in the liver and plasma free fatty acids. Hence, the hypoglycemic (blood sugar lowering) effect of onion solid waste extracts might be due to lipid metabolism, reduced oxidative stress, and modulated proinflammatory cytokines.1 However, please consult a doctor for proper diagnosis and treatment of diabetes. Do not self-medicate.

7.  Potential uses of onion as an antioxidant:

According to studies, onions may have antioxidant potential due to high levels of organosulfur compounds, polyphenols, and flavonoids, all of which are natural antioxidants. The study reports revealed that onion had higher antioxidant activity despite having lower organosulfur levels than garlic.2

8.  Potential uses of onion for the bone:

A study has investigated the effect of onion on osteoporosis, which is characterised by bone mineral density reduction. The cell line investigations revealed that onion extract might inhibit osteoclastogenesis (formation of bone-resorbing cells, osteoclasts) process. According to another study, postmenopausal women supplemented with onion juice had increased bone marrow density.2 Therefore, onion might be helpful for bone.

9.  Potential uses of onion for inflammation:

In an animal study, a red onion bulb extract might help reduce lymphocyte and eosinophil numbers (inflammatory cells) in the blood and bronchoalveolar lavage fluid (fluid collected from the lungs). Another study showed that onion extract reduced proinflammatory cytokines in microglia (brain) cells, hence might help against brain inflammation.2

The onion bulb extracts might reduce the overall counts of white blood cells and lung inflammatory cells, such as eosinophils, neutrophils, and monocytes, in animal models.2 Therefore, it might be helpful for inflammation.

10. Potential uses of onion for the liver:

Researchers studied the effects of onion extract on liver damage in animal models. Onion apparently reduced alanine aminotransferase and total serum bilirubin levels but did not affect aspartate aminotransferase, alkaline phosphatase, or lactate dehydrogenase levels. This may indicate that onion extracts may have possible liver protective effects.2 However, more research is required to prove these possible effects.

Though there are studies that show the potential uses of onion in various conditions, but these are insufficient and there is a need of further studies to establish the true extent of benefits of onion on human health.  

Studies imply that onion is a good source of a flavonoid called quercetin, a powerful antioxidant. It is mainly found in the skin of the onion and has various health benefits. It might be useful in reducing cholesterol, avoiding blood thinning and clotting, and fighting asthma, diabetes, and other infections. It might also exhibit antiviral, antibiotic, anti-inflammatory and sedative properties.

Dr. Rajeev Singh, BAMS

Also Read: Dhania (Cilantro): Uses, Benefits & Side Effects

How to Use Onion?

Onion can be used in the following ways::

  • Onion skin1
  • Onion peel extract
  • Onion bulb extract
  • Green onion bulbs
  • Onion juice
  • Onion dry powder
  • Onion leaves
  • Onion sprouts2

You must consult a qualified doctor before taking any herbal supplements. Do not discontinue or replace an ongoing treatment of modern medicine with an ayurvedic/herbal preparation without consulting a qualified doctor.  

Also Read: Shallots vs Onions: Breaking Down the Differences and Nutritional Value

Side Effects of Onion:            

There are no major side effects of onion reported by far. If you experience any side effects, seek immediate medical help from your doctor who has prescribed it to you. They will be the best guide for providing proper treatment to overcome side effects.

Also Read: White Onion: Exploring its Unique Benefits and Nutritional Profile

Precautions to Take With Onion:

Onion is a regular food item but if you plan to take onion for its health benefits you should follow general precautions. Safety studies of onion on pregnant and breastfeeding women have not been documented. Likewise, no research on the safe use of onion in children has been documented. Therefore, it should only be taken under the supervision and advice of a physician.

Interactions With Other Drugs:

There is not much information available on how onion interacts with other medications. Hence, one should consult a doctor before taking onion if they take any other drug or supplement.

Also Read: Barley: Uses, Benefits & Side Effects

Frequently Asked Questions:

What is onion (Pyaaz)?

Onion is a perennial herb with an underground bulb and a stem.2

Is onion a vegetable?

Yes, it isthe most widely farmed and consumed vegetable worldwide.1

Is onion good for weight loss?

Yes, onion might help in weight management . The presence of quercetin in onion exerted anti-adipogenetic (inhibition of formation of fat cells) activity in an animal study.1 There is a requirement for more research to scientifically back up such claims.

Is onion good for diabetes?

Onion might be helpful for diabetes. Onion extracts might have a blood sugar lowering effect by potentially inhibiting α-amylase and α-glucosidase enzymes.1 Kindly ensure that you consult a doctor for proper diagnosis and treatment of conditions like diabetes.

Is raw onion good for health?

Raw onion might be good for health.It might be helpful for diabetes, cardiovascular illness, and stomach cancer.2 However, the potential uses of raw onion for health need to be ascertained by more research. Consult a doctor before using onion for its health benefits.

What is the chemical composition of onion bulbs?

Onion bulbs and leaves contain many phytoconstituents such as cyaniding glycosides, prostaglandins, quercetin, sterols, phenol compounds, catechol, protocatechuic acid (in the dried brown outer scale), and diosgenin (in the blossoms and bulbs) and nutrients like proteins, fats and carbohydrates.3

Is onion good for the liver?

Onion might be good for the liver. Onion extracts were found to have potential liver-protective effects by probably helping lower the levels of serum enzymes such as alkaline phosphates, aspartate aminotransferase and alanine aminotransferase in an animal model.2 more research is needed to prove such claims. Therefore, kindly consult a doctor for liver disease and do not self-medicate.

Is onion oil good for hair growth?

Onion might be helpful for hair growth. According to a study, the topical application of onion juice may be beneficial for patchy alopecia (hair loss) as it might help in the growth of coarse terminal hairs.6 However, such effects need to be proved by more.


  1. Kumar M, Barbhai MD, Hasan M, Punia S, Dhumal S, Rais N, et al. Onion (Allium cepa L.) peels: A review on bioactive compounds and biomedical activities. Biomed Pharmacother. 2022; 146: 112498. Available at: https://pubmed.ncbi.nlm.nih.gov/34953395/
  2. Chakraborty AJ, Uddin TM, Zidan M, Redwan BM, Mitra S, Das R, Nainu F, Dhama K, Roy A, Hossain M, Khusro A. Allium cepa: A Treasure of Bioactive Phytochemicals with Prospective Health Benefits. Evid-Based Complement Altern Med. 2022; 2022: 1-27. Available at: https://www.hindawi.com/journals/ecam/2022/4586318/ 
  3. Battagani D, Jada Naga L, Rayadurgam N. Review on Phytochemicals and Pharmacological Studies of Allium cepa (Onion). Int J Pharm Sci Rev Res. 2021; 68(1): 85-91. Available at: https://globalresearchonline.net/journalcontents/v68-1/15.pdf 
  4. Sidhu JS, Ali M, Al-Rashdan A, Ahmed N. Onion (Allium cepa L.) is potentially a good source of important antioxidants. J Food Sci Technol. 2019; 56(4): 1811-1819. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6443770/
  5. Bora K, Sharma A. Phytoconstituents and therapeutic potential of Allium cepa Linn.-A Review. Pharmacog Rev. 2009; 3(5): 170-180. Available at: https://www.phcogrev.com/sites/default/files/PhcogRev-3-5-170.pdf
  6. Semalty M, Semalty A, Joshi GP, Rawat MS. Hair growth and rejuvenation: an overview. J Dermatol Treat. 2011; 22(3): 123-132. Available at: https://pubmed.ncbi.nlm.nih.gov/20536276/

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