Skin

"The skin is the largest organ of the body, with a total area of about 20 square feet. The skin protects us from microbes and the elements, helps regulate body temperature, and permits the sensations of touch, heat, and cold.
Skin has three layers: The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.
The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands.
The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue.
The skin’s color is created by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermis."

Pellagra

Pellagra is a disease that affects your digestive system, skin, and nerves, resulting in dermatitis, diarrhea, and mental disorders. The most common cause of pellagra is not having enough niacin (primary pellagra). Other causes of pellagra are associated with digestive disorders that reduce the absorption of niacin in your body. Some people with pellagra have mild symptoms, such as fatigue, while others may develop severe depression and anxiety. Fortunately, pellagra can be treated with nutritional supplementation to resolve deficiencies in niacin. Lifestyle changes can reduce your risk for pellagra and include limiting alcohol intake, eating a well-balanced diet, not smoking, and always taking all medications and supplements as prescribed.