Define the effect of niacin deficiency on Skin?

Dermatitis is the characteristic feature of the' disease, It is symmetrical in distribution. In early stages, a bright red erythema resembling sunburn occurs over the exposed parts of the body. The common sites are the face, neck and  on the extremities such as the back of the fingers, hands, wrists and elbows, the  forearms, dorsum of the feet, knees and ankles and the neck. In the beginning, the skin is red and slightly swollen, as illustrated in Figure 8.5. The lesion may worsen by the formation of vesicles and bullae with cracking of the skin.  Secondary infection is always present. With improvement, the skin becomes dry, less red and the surface desquamates. The dermatitis is precipitated with exposure to sunlight.