Onion juice contains lots of sulfur, selenium, minerals, B vitamins and C vitamins which are very good for hair growth. This aids faster and denser growth of eyebrow hair. Sulfur improves the production of collagen tissues required for proper eyebrow growth. Also, it strengthens the hair follicles. As onion has a pungent smell, it is best to use lemon juice to remove all traces of the smell. Apply onion juice to your eyebrows every alternate day.