Final answer:
Alopecia is an autoimmune disorder where the immune system damages the hair follicles, causing hair loss. It is not caused by increased blood circulation, overactive sebaceous glands, or solely by UV radiation exposure.
Step-by-step explanation:
The cause of Alopecia is C. Immune system attacks hair follicles. Alopecia is an autoimmune disorder where the immune system mistakenly targets and damages the hair follicles, leading to hair loss. Unlike normal biological processes in which anagen is the active phase of the hair growth cycle and sebaceous glands secrete sebum for lubrication, in Alopecia, the immune response disrupts this cycle. Factors that can lead to Alopecia may include genetics, environmental triggers, and stress; however, it is not caused by increased blood circulation, overactive sebaceous glands, or UV radiation exposure alone, albeit these factors might affect the overall health of the skin and hair.