Aloe is used to help keep skin healthy and moist, which in turn makes for better healing. In addition, it contains Lignins, an integral part of cell walls so that skin heals faster. Aloe also contains a cooling agent, salicylic acid, which helps sooth the pain of sunburns.

zehwang is correct.  To elaborate, per the botanicals link below, Aloe has the unique ability to help skin rejeuvenate itself by stimulating cellular metabolism.  This creates an "oxygen exchange" thereby increasing the absorbtion of healing nutrients from the aloe into the skin.  Vitamins A and C, copper, selenium, magnesium, zinc all occur in Aloe which make it good for fighting viruses as well.  See the link below for more information, and for other natural healing methods.