The subcutis is not a layer of the skin but rather the layer of fat and connective tissue beneath the skin.

The epidermis is the outermost layer of the skin and its primary function is to protect the body from external factors such as microorganisms, chemicals, and UV radiation.

Melanocytes are specialized cells found in the epidermis that produce melanin, the pigment that gives skin, hair, and eyes their color.

Hair plays a crucial role in thermoregulation by providing insulation and helping to maintain body temperature.

Sebaceous glands are not sweat glands but rather oil glands that secrete sebum, a waxy substance that helps to lubricate the skin and hair.

Nails serve primarily to protect the fingertips and toes from injury and wear.

Vitamin D is synthesized in the skin upon exposure to sunlight and is essential for calcium absorption and bone health.

Dermatitis is a general term for a skin rash or inflammation of the skin.

Herpes simplex is a viral infection that can cause blisters filled with fluid, typically around the mouth or genitals.

Basal cell carcinoma is the most common type of skin cancer, characterized by the uncontrolled growth of basal cells in the epidermis.

Excretion is not a function of the skin. The skin is responsible for protection, sensation, thermoregulation, and vitamin D synthesis, among other functions.

The stratum corneum is the outermost layer of the epidermis and consists of dead, flattened cells filled with keratin.

Keratinocytes are the most abundant cell type in the epidermis and are responsible for producing keratin, the protein that gives skin its strength and flexibility.

The dermis is the layer of skin beneath the epidermis and contains blood vessels, nerves, hair follicles, and sweat glands. It is responsible for sensation, thermoregulation, and nutrient supply to the epidermis.

Actinic keratosis is a precancerous skin condition caused by excessive sun exposure, but it is not a type of skin cancer.