Contrary to popular belief and opinions of some experts, moisturizing is not a universal "must do" of basic skin care. Not everyone needs moisturizing. In fact, poorly selected and misused moisturizers may do more harm than good.
People with oily skin do not need to moisturize because the abundant sebum they produce has more than sufficient emollient and moisturizing effect. People with normal skin do not necessarily need to moisturize since they too produce enough sebum and other natural emollients and humectants. Under some circumstances (e.g. dry climate, frequent water exposure, etc.) people with normal skin may want to apply an oil-free moisturizer after cleansing to prevent the development of dry skin. Moisturizing does benefit dry skin (and dry areas of combination skin) by improving the skin's barrier function, reducing irritation, sensitivity as well as creating a plushier look. However, moisturizing alone does not seem to have a major impact on the development (and prevention) of wrinkles and other signs of skin aging.
If you feel you need to moisturize, make sure you pick the right type of moisturizer for your skin type. Otherwise you may do more harm than good.
Emulsion based moisturizers
Water and oil do not dissolve in each other. When they are mixed together and shaken they form a fine mixture of oil droplets in water or vice versa (depending on the proportions used). Such mixtures can be stabilized with so-called emulsifiers, which are surfactants preventing water and oil droplets from coalescing. Both oil-in-water and water-in-oil emulsions may be useful for dry skin that produces too little sebum, which is particularly common in women during and after the menopause. Moisturizers based on oil-in-water emulsions tend to be heavier but may be a good fit for some cases of particularly dry skin. Oil-water emulsions tend to be more comedogenic than oil-free moisturizers and should not be used for normal or oily skin.
The idea of an occlusive moisturizer is to cover the skin with a waterproof film through which water cannot evaporate or otherwise escape. Occlusive ingredients include petrolatum (a.k.a. Vaseline), mineral oil, siloxanes (dimethicone, cyclomethicone) to name a few. Occlusive ingredients may clog pores and produce other unwanted effects. Siloxanes tend to cause fewer breakouts than petroleum-based ingredients but individual reactions vary. Occlusive moisturizers should be considered for dry skin unresponsive to moisturizers based on oil-water emulsions. This may happen when the primary cause of dryness is excessive water evaporation from the skin surface. In such a case, an occlusive moisturizer, particularly one with a siloxane, may be a better alternative. It is best to apply an occlusive moisturizer over moist skin.
Oil-free moisturizers are usually based on the so-called humectants, the substances that can trap and hold water. Some examples include propylene glycol, glycerin, sodium PCA, hyaluronic acid, colloidal oatmeal, collagen and others. If you have oily or normal skin and feel the need to moisturize, use an oil-free moisturizer.
In some cases of dry skin or in very dry environments, ordinary moisturizers just don't cut it. They last for an hour or two and then your skin gets as dry as before. Specially designed long-lasting moisturizers are a viable alternative to having to reapply a moisturizer every two hours. Long-lasting moisturizers usually combine active principles from several types of moisturizers. A typical long-lasting moisturizer may contain several humectants and occlusive agents (e.g. dimethicone, colloidal oatmeal, glycerin, sodium PSA, hyaluronic acid, petrolatum and so forth). Oftentimes, long-lasting moisturizers is an overkill but may be just right for some cases of severe dryness.
Moisturizers as vehicles for active ingredients
Whether to use a basic moisturizer is becoming a moot point, at least as far as facial skin care is concerned. These days most people use advanced skin care products with active ingredients aimed at preventing or reducing the signs of skin aging. It is often redundant and counterproductive to apply both a moisturizer and an anti-aging product. Besides, most anti-aging products contain some moisturizing ingredients. People with oily and normal skin can forego basic moisturizers and use anti-aging products only. Dry skin sufferers may be able to do the same by picking an anti-aging product with a sufficiently moisturizing base. In the remaining cases of severely dry skin, a moisturizer should be applied a few minutes after the anti-aging product (to allow active ingredients to absorb).
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