Hair changes can be reversible while others are permanent. Hair color can be back after some time because of the re-growth of melanocytes. Hair growth is being affected by several factors such as family history of hair loss, hormonal changes or lack of nutrition. Hair loss can be temporary or permanent. It can be reversible even without treatment if the condition is a result of alopecia areata or patchy hair loss. It can be permanent if it is hereditary.
The difference between naturally curly hair and naturally straight hair is the presence of disulfide bonds. Curly hair has more disulfide bonds than straight hair. These bonds keep the hair in the shape it was formed. Alteration can happen only by way of perming or relaxing.