What are the major functions of skin?

Keeping bacteria out - Most germs cannot cross this flesh barrier unless there is a break due to a cut, scratch, or the bite of an insect or animal.  Our hands are usually covered with germs because we constantly use them to hold money, shake hands, and open dirty doorknobs.  Washing your hands with soap can reduce the number of bacteria by more than 99%.  There are several bacteria and fungi that live on normal healthy skin.  These "freeloaders" actually help us by using all of the nutrients available so other disease-causing microorganisms can't grow.  The skin also secretes a weak acid that can deter growth of some bacteria and fungi. 

Holding water in - Our bodies contain about 80% water and this water is critical for survival.  Without skin, water would evaporate quickly and good stuff (like protein) would leak out.  The major risks after severe burns that destroy skin are dehydration, loss of protein, infection and imbalance of electrolytes.  Premature infants have thin skin and can lose water through the skin rapidly.

Touch sensation - Skin helps use feel temperature (hot and cold), vibrations, pain, and soft touch.  Without pain sensation in the skin, we would constantly damage ourselves without realizing it, creating entry points for germs.

Protection from the sun - Pigment in the skin protects our bodies from the sun's rays.  Too much sun leads to skin damage (i.e., sunburn).  Some sunlight is needed to convert some chemicals to vitamin D, which is important for bone development.

Temperature regulation - Ever wonder why your cheeks turn red when you exercise on a hot day.  In addition to sweating, skin helps get rid of excess heat from the body by widening the blood vessels near the surface of the skin (i.e., capillaries) so heat can be released more easily.  This gives skin a red or pink appearance.

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