Here come some benefits of onion to the skin. Onions can be really good for your skin even though they are not usually added to most skincare products. Their nutrient richness makes them useful for a variety of benefits. Here are some ways onions can help benefit your skin:
Antioxidant: 

Onions contain high levels of antioxidants that protect the skin against free radicals. This can cause a loss of elasticity and wrinkles, making the skin look aged much earlier than it actually is.
Antibacterial properties: 

Onions possess antibacterial property. This might avoid infection and acne breakouts.
Reduce scarring: 

According to some scientists, it aids in reducing scarring due to onion extracts.
Brighten your skin: 

Onions may even make your skin look much brighter. Onion is also a good source of vitamin C. This vitamin increases the cell turn over which ultimately decreases break outs, reduces redness and glows the skin.

Reducing the acne

Diluted Sulfur is used to treat some types of acne. Good news is that onion contain natural sulfuric acid.Many companies use the onion juice in over-the-counter acne products.
Promotes hair growth. 

Though no research was done yet, for some, onion juice is true about helping growth in hair scalp.

Topical application: You can apply onion juice directly to your skin, and another use for it is by adding it into homemade face mask or scrubs.
Dietary intake: You can also derive onions as part of your healthy diet for your skin.
Note: Onions, in general, have been known to offer various benefits for skin health; however, a patch test should always be done on any new skincare product being used for its potential onion content. Individuals with sensitive skin or other skin conditions should consult a dermatologist before using onion-based products.