In this month's Cosmetic Conundrums column, Dermatology Times® Chief Medical Editor Zoe Diana Draelos, MD, discusses allergies from skin care products and how to prevent adverse reactions.
Q: How do manufacturers test cosmetic products for irritant and allergic contact dermatitis?
Most products consumers buy will have been tested by the manufacturer for possible allergy and irritancy. The Human Repeat Insult Patch Test (HRIPT) is the industry standard for new product testing.
If testing is done, then how do problematic products enter the marketplace? The answer lies in understanding how HRIPT is conducted. A breathable patch with the product under review is placed on a study participant’s upper back and changed every Monday, Wednesday, and Friday for 3 weeks. The participant is then given a rest period and rechallenged. Usually, a negative control patch that contains nothing and a positive control patch that contains sodium lauryl sulfate also are placed on the participant’s upper back.
Unfortunately, this type of testing has limitations. For example, the upper back has some of the thickest and most resilient skin on the body. The skin on the back may not react, but the skin around the eyes can demonstrate irritancy. It is not possible to do patch testing around the eye, so the back serves as surrogate. Another limitation of HRIPT is the panel selection. Over time, most contract research centers develop panels of participants with robust skin. As you might imagine, a participant who experienced a poor outcome probably would not volunteer again. Further, many of the HRIPT centers are located close to college campuses and use young individuals with healthy skin. All these factors limit the sensitivity of HRIPT and may not uncover issues that arise in the general population.
Q: How should patients screen their new cosmetic purchases to prevent adverse reactions?
Simple, at-home testing can prevent overall facial irritation problems with new cosmetics. It is easy to teach patients with sensitive skin how to conduct the testing. Instruct the patient to apply a small amount of the cosmetic in the antecubital fossa for 7 nights in a row before going to bed. If no problems arise, the product then can be applied to the posterior ear for 7 nights in a row before going to bed. If there are still no problems, the patient may apply the product to their face, avoiding the eyes, for 7 nights. If no irritation or allergy occurs, the product can be applied to the entire face.
If problems arise, advise the patient to have more formal patch testing done under the dermatologist’s direction. This testing method only examines final formulations and will not detect specific ingredient allergies.
Q: What ingredients in cosmetic products are most likely to produce irritant contact dermatitis?
Emulsifiers are the most irritating substances placed in cosmetic products. They are found in all formulations that contain hydrophilic (water loving) and hydrophobic (water hating) ingredients. Most cosmetic products are oil-in-water emulsions in which the oil is emulsified into the higher concentration dominant water phase. These emulsions tend to leave less residue on the skin and consequently dry more quickly as the water evaporates.
Emulsifiers are basically detergents that keep the oil and water from separating. All oil-in-water emulsion moisturizers contain small amounts of detergents that also emulsify the intercellular lipids and sebum. This is where the barrier breakdown occurs and the induction of irritation begins. Fortunately, the concentration of the emulsifier is usually small and carefully selected to avoid this problem. For people with extremely sensitive skin, it is best to recommend a moisturizer that is free of emulsifier. These would be ointment formulations that do not contain water. Although they are not as aesthetically pleasing as oil-in-water emulsion lotions, they will not incite irritant contact dermatitis.
The second most common problematic ingredient in moisturizers is the preservative. All water-containing moisturizers must contain a preservative because water supports microbial growth. Preservatives are not skin-friendly ingredients; their sole role is to kill bacteria. Ointments that do not contain water do not need to have high preservative concentrations and may need only antioxidants to prevent oxidation of the lipids resulting in rancidity. Here again, an ointment is the best choice to avoid problems in patients with extremely sensitive skin.