Skin is the largest organ in human body. It is made up of two main layers which are further divided into sub layers.
1. The upper layer is called ‘epidermis‘. The lower layer of the epidermis (upper layer) is called as the basal layer. The basal layer contains tiny parts ‘melanosomes’. These melanosomes contains the cells that give skin its color. These cells are called melanocytes. The melanocytes produce a pigment (color) called ‘melanin’. The melanin is the main factor in defining the skin color. The more the melanin the darker the skin color. Melanin is also present in the other layers of the epidermis. The thickness of epidermis, blood color, the vascularity of epidermis also affects the skin of color to some extent.
2. The lower layer is called ‘dermis‘.

There are diseases that increase the skin color and there are diseases that reduce the skin color. Diseases that cause reduction of skin color are call hypo pigmentation. Here is a short list for these.

• Vitiligo : This is the most common autoimmune diseases which cause de pigmented patches. Vitiligo is the most noticeable and wide spread skin disease.

• secondary leucoderma : This occurs due to certain chemicals phenol derivatives
• Post inflammatory hypo pigmentation : It happens after the healing phase of psoriasis, eczemas.

• Pityriasis alba : this is often observed on the face and usually in young children in winter.

• Pityriasis versicolor : It is a fungal infection caused by ‘pityrosporum orbiculare’ which is a type of yeast.

• Leprosy : It is a chronic disease affecting mainly the skin and nerves. It is curable with drugs.

• Nevus depigmentosus : these are the hypo pigmented patches that are present at birth.

Pityriasis Alba

Pityriasis-Versicolor

Leprosy

Nevus Depigmentosus