Healthy hair is more than just what we put on our hair and scalp - it encompasses a range of different internal and external factors.
External factors are made up of things outside of the body, such as the products that we apply on our hair and scalp, heat styling, and exposure to UV. 
Internal factors are made up of processes occuring within our body such as any underlying health conditions or illnesses, our diet and the foods we eat, and genetics passed down from generations. 
All these factors together influence how our hair looks and feels, and can contribute to hair and scalp conditions like hair loss/thinning, hair breakage, and more.