Physiology

Skin performs, or participates in, a host of vital functions and functions best when well hydrated. Well-hydrated skin supports ideal skin pH between 4.0 and 6.0. Alterations in skin pH increase susceptibility to infections. Damage to skin impairs its ability to carry out the many important functions of the skin.

Functions of the skin

Function		Description
	*Protection*	Acts as a physical barrier to microorganisms and foreign matter Protects the body against infection from the environment with the Langerhans cells (triggers immune system) Protects underlying tissue and structures from mechanical injury Prevents the loss of electrolytes, heat, water, proteins, and other substances to maintain homeostasis
	*Sensory perception*	Contains nerve endings and sensory receptors (Merkel's cells) Allows for perception of pain, pressure, heat, and cold to identify potential dangers and avoid injury
	*Thermoregulation*	Contains nerves, blood vessels, and eccrine glands in the dermis to control body temperature Causes blood vessels to constrict (reducing blood flow and conserving heat) when exposed to cold or internal body temperature falls Causes small arteries in the skin to dilate and increases sweat production to promote cooling when skin becomes hot or internal body temperature rises
	*Excretion*	Transmits trace amounts of water and body wastes to the environment Allows the skin to maintain thermoregulation and electrolyte and hydration balances Prevents dehydration by ensuring that the body doesn't lose too much water
	*Metabolism*	Helps to maintain the mineralization of bones and teeth Synthesizes vitamin D (which is crucial to the metabolism of calcium and phosphate) when exposed to the ultraviolet spectrum in sunlight
	*Absorption*	Allows for the absorption of some drugs directly into the bloodstream

Aging and skin function

With aging, the skin undergoes a number of changes that increase the risk of wound development and impair the ability of wounds to heal. Skin changes begin at birth and continue throughout the lifespan. Aging skin loses firmness and elasticity related to changes in collagen and elastin production.

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