Onion shampoos are a rich source of antioxidants. Their antimicrobial nature treats dandruff, irritation, and other scalp problems. The sulfur in the onion helps maintain thick hair, reduce hair loss and boost hair development. The high sulphur levels also help to prevent hair loss and strengthen hair follicles. Sulfur is a key component of keratin, which is the protein that makes up hair. Onion extract is a good source of sulfur, so it may help to strengthen hair and reduce breakage and hair loss. Onion extract has antibacterial and antifungal properties, so it may help to soothe an itchy scalp and reduce dandruff. Some studies have shown that onion extract can stimulate hair growth.