Onions do not grow hair. Onions are vegetables, and hair is a characteristic of mammals. This question plays on the common misconception that rubbing onion on the scalp can promote hair growth.
While some people believe this, there is no scientific evidence to support this claim.
The idea likely stems from the fact that onions contain sulfur compounds, which are also found in some hair growth products. However, these compounds do not directly stimulate hair growth.
It is important to rely on scientifically proven methods for hair growth, such as maintaining a healthy diet, using hair growth products with proven ingredients, and consulting with a dermatologist for personalized advice.
