Moisturizers - are they harmful to the skin's natural hydration
It's probably key to understand how the skin functions. Normal skin has oil producing sebaceous glands that naturally lubricate the skin and keep it properly hydrated by preventing excessive water loss or absorption. Natural moisturizing factors (NMF) are free amino acids and other chemicals present in the stratum corneum that are responsible for keeping the skin moist and pliable by attracting and holding water, a property called hygroscopic.
The major factor responsible for dry, scaly skin can therefore be related to the loss of water from the stratum corneum, which fluctuates with environmental humidity levels, damage to the barrier by denaturing keratin protein, removing NMF and interrupting lipid bilayers. Dry skin arises from distress or damage to the skin's lipid barrier - structural deterioriation exposes skin cells to external threats and contributes to trans-epidermal water loss (TEWL) as cells become dehydrated. This could also occur from using solvents, detergents, excessive use of water and soap and other irritating chemicals.
Moisturizers work to prevent water loss by coating the skin with a substance to trap moisture - replicating what the healthy sebum balance does normally. Studies show that for dry skin syndromes like xerosis, moisturizers are effective. But some believe that topical hydrators should support the natural hydration process rather than simply supplementing moisture. The moisturizer may offer temporary relief, but the cell disruption must be isolated and corrected for dry skin to actually be alleviated.
Regardless, how, then, would moisturizers themselves be harmful to the natural hydration process? Dermatologist Dr. Zein Obagi says that when cells recognize that an outside source has already hydrated the skin, there's no need for natural hydration to take place. This means that the cells become inactive and stop the moisture production process, which leads to dry skin. The doctor likens it to a moisturizer addiction.
Dr. Hauschka has a similar theory. He advises against using a night cream because regular application interferes with the tasks your skin undergoes at night like regenerating, balancing oil production and expelling impurities. Based on this theory, regular application over time means that the skin becomes less able to care for itself.
Studies do show that over time, moisturizer use has an impact on the skin. A study from the University of Copenhagen confirmed that skin barrier function could be adversely affected by use of moisturizers. In the study, transepidermal water loss was significantly higher on the arm treated with moisturizer than on the control arm, which suggests that long-term treatment with moisturizers on normal skin may increase susceptibility to irritants. But, it isn't quite clear if the natural hydration process is quelled because of the moisturizers' regular hydration or if the other ingredients in them are simply damaging the cells and causing irritation.
A study in the American Journal of Clinical Dermatology suggests that certain types of emulsifiers may weaken the skin barrier. Other studies pose questions as to whether moisturizers' inherent capacitance is a source of false positive results.
Too much moisturizing comes with other problems as well. Oil based moisturizers can run the risk of clogged pores and water-friendly ingredients like glycerin, which is supposed to attract and retain moisture, can only do so at a level of humidity above 70%.
The key may be to not overuse moisturizer if it isn't needed. For those of us with normal skin, developing a dependence on moisturizer is just not necessary, especially when our complicated epidermis has the functions in place to keep us hydrated and well. And for those prone to dry skin, it may be necessary to find a deeper solution than just slopping on a standard moisturizer.