You've probably been advised to moisturize your skin - by friends, family, your dermatologist or the many advertisements for skin care products - but you may be wondering why moisturizers are so important. The basic function of moisturizers is to help treat your skin when it's dry and prevent it from drying out again. Moisturizers do this by holding water in the stratum corneum, the outermost layer of the skin [source: Mayo Clinic]. But they have other functions as well. They can help protect your skin from the environment -- applying moisturizer creates a barrier on your skin that keeps oils from escaping and harmful outside elements from causing dryness or irritation.