Definition: The term "What makes hair turn red?" refers to the color change that occurs when hair follicles release an enzyme called melanin, which can be turned into a darker shade by the presence of oxygen. The precise definition of what causes this specific type of skin pigmentation is complex and depends on the individual. Some theories suggest it may be caused by changes in the production or metabolism of melanin, while others explain it as a side effect of certain medications or conditions like celiac disease. In general, hair turn red refers to an increase in melanin levels in the hair follicles, which is a natural part of the body's defense mechanism against harmful UV rays. This color change typically begins when the hair starts growing and can occur at any point in its lifecycle. Understanding the specific cause for this phenomenon is important for skincare professionals who work with hair care products, as well as those caring for patients with skin conditions like dermatological conditions or certain medications that may alter hormone levels or vitamin D levels.