Option 1: Aging of epidermal cells is not the direct cause of grey hair. While it is true that as we age, the production of melanin decreases, leading to greying hair, it is not the aging of the epidermal cells themselves that causes this change.

Option 2: The death of dermal cells also does not directly cause grey hair. Grey hair occurs when there is a decrease in melanin production, which is primarily produced in the hair follicles and not the dermal cells.

Option 3: The loss of sebum in epidermal cells is not the cause of grey hair. Sebum is an oily substance produced by the sebaceous glands and helps to moisturize and protect the hair. Its loss does not directly impact melanin production.

Option 4: This is the correct answer. Grey hair is caused by the loss of melanin in the epidermal cells. Melanin is the pigment responsible for giving hair its color, and a decrease in its production results in grey hair.