Dry skin is a condition involving the integumentary system and occurs from reduced activity of the sebaceous glands. Dry skin occurs most commonly on the scalp, lower legs, arms, hands (Pic. 1), the knuckles, the sides of the abdomen (Pic. 2), and thighs. Symptoms most associated with dry skin, scaling (the visible peeling of the outer skin layer), itching, and skin cracking (Pic. 3).

In healthy skin, the outer most layer of our skin is composed of dead cells called the stratum corneum (Pic. 4). These cells are cemented together to form a protective barrier for the alive cells underneath. Normally this layer of skin has the same surface area as our epidermis (the layer directly underneath the stratum corneum). However, when the skin dries out, the stratum corneum shrinks creating that cracked alligator skin. 

Its pathogenesis has been suggested to include changes in the nutrient supply of the skin, and in the production of sweat and oil in the skin.It happens more often in the winter where the cold air outside and the hot air inside creates a low relative humidity. This causes the skin to lose moisture and it may crack and peel. Bathing or hand washing too frequently, especially if one is using harsh soaps, can contribute to dry skin. Dry skin can be caused by a deficiency of vitamin A, vitamin D, systemic illness, severe sunburn, or some medication. Detergents such as washing powder and dishwashing liquid can cause xeroderma. Dry skin has also been related to certain effects on the mast cell population of the skin and to the decreased skin innervation caused by AIDS (Acquired Immune Deficiency Syndrome). 

A physician often can diagnose dry skin by looking at the skin. A family history is very useful. In some cases, a skin biopsy is done to help to confirm the diagnosis. In some instances, genetic testing may be helpful in making a diagnosis.

In most cases, it can safely be treated with emollients or moisturizers. As a preventive measure, such products may be rubbed onto the affected area as needed (often every other day) to prevent dry skin. The skin is then patted dry to prevent removal of natural lipids from the skin.

Thyroid disorders

The functioning of the skin depends on the general status of the body and it is controlled by hormones, like the thyroid. Low thyroid function (hypothyroidism) can be associated with skin disorders due to reduced blood supply such as dry skin.

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The Science Behind Dry Skin ―by Jean Welsch licensed under CC BY-NC 3.0
Xeroderma ―sourced from Wikipedia licensed under CC BY-SA 3.0
New insights into HIV-1-primary skin disorders ―by Cedeno-Laurent et al. licensed under CC BY 2.0
Ichthyosis ―sourced from Wikipedia licensed under CC BY-SA 3.0
Structure of the skin ―by OpenStax College licensed under CC BY 3.0
Dry Skin ―by DePootisMan licensed under CC0 1.0
Ichthyosis ―by Henry Fox licensed under CC0 1.0
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