To maintain healthy, happy skin, you must seal in your hydrating gel with a moisturizer every night and a moisturizer and/or sunscreen during the day. This technique works much like a greenhouse: after watering plants, one covers them with plastic to prevent the water from evaporating. Similarly, without preventative action, water can and will evaporate through the skin. This problem is called transepidermal water loss or "TEWL." Moisturizers help prevent TEWL.

The skin loses a lot of its natural moisture through evaporation and is particularly affected by extreme temperatures, sun exposure, wind exposure, and drying (low humidity) conditions found in buildings with central heating and in airplanes. Using harsh soaps, astringents, or medications also affects the skin'€s moisture. To counteract these factors, the skin needs a moisturizer with the correct proportions of water and oil to form a suitable barrier.

For best results, you should apply moisturizers to skin that's still damp from cleansing or toning. Applying moisturizers to damp skin ensures the skin can hold more water; this temporarily plumps up fine, parched lines. Moisturizers also protect your skin against environmental pollution and free radical attack, which leads to aging. You may require different moisturizers for day use and night use or for different times of the year.