From Dark to White to Dark Again: What causes transient colour changes?

Short term Hair Colour Changes

They greying of hair is common. By age 50, about 50 % of people have at least half of their hairs appearing grey/white. This type of hair colour change is permanent - and the only way most people can achieve a darker colour is through the dyeing of hair. 

A different scenario exists with individuals noticing that their hair has turned white only to notice that it turns back to the original colour again within months of noticing it.  There are a variety of causes of this phenomenon, especially when it occurs in one area compared to if it occurs all over the scalp. The most important conditions to consider in transient hair greying/whitening are the autoimmune conditions alopecia areata and vitiligo. Other issues to consider include thyroid abnormalities, pituitary problems, and deficiency of vitamin B 12.   Deficiencies of iron, calcium and vitamin D as well as pregnancy and systemic illnesses need to be considered by are uncommon causes.