Because the category is so broad, Dr. Wu says it's impossible to generalize about the effect the products have on the skin barrier function. The problem is exacerbated by the fact that manufacturers are not required to test for the safety or efficacy of their products.
National report - It's hard to make a general statement about the effect of cosmeceuticals on skin barrier function because it's hard to define the word "cosmeceuticals."
"I think of the definition in very literal terms - a cosmeceutical is an over-the-counter product that has the characteristics of cosmetics and pharmaceuticals just as the name implies. It has the properties of a cosmetic because it is applied topically and is designed to improve the appearance of the skin, but like a pharmaceutical, it presumably has the ability to affect the structure and/or the function of the skin."
Dr. Wu says, although cosmeceuticals can have other uses, the general perception is as anti-aging products. However, the category can also include products like hydroquinone 2 percent, which is used for the gradual lightening of hyperpigmented skin.
Because the category is so broad, Dr. Wu says it's impossible to generalize about the effect the products have on the skin barrier function.
The problem is exacerbated by the fact that manufacturers are not required to test for the safety or efficacy of their products. Although she says good companies and physician-developed lines are usually quality-controlled, many products made by smaller companies are not necessarily standardized.
"A lot of these are from plant-based ingredients that have hundreds of suppliers around the world and may have no verifiable or consistent strengths. There are a lot of unknowns - it's like the Wild West of skincare," Dr. Wu says.
There are some general characteristics of cosmeceuticals, however, that have disparate effects on the skin.
Retinoids and alpha hydroxy acids are the active ingredients in many anti-aging cosmeceuticals and may be able to effect skin cell structure and function according to Dr. Wu.
"We do know that retinol can increase the turnover of the skin cells, which can make the skin more susceptible to sun damage - and more vulnerable in general.
"When the barrier is altered you get little cracks. Just as over-washing can cause microscopic cracks in the skin, which can expose the nerve-endings making the skin more sensitive to ingredients that ordinarily wouldn't be irritating," she explains.
In the case of cosmeceuticals, it is that action by the active ingredients that increases cell turnover or epidermal shedding - making the skin look and feel smoother and less dull - improving the appearance of the skin.
But these ingredients can also irritate the skin. To combat this, often the cosmeceutical vehicle is designed to protect the skin barrier.
"If you incorporate the active ingredient in a vehicle, which will hold the water in and help restore the skin barrier, then presumably the effect is neutral. That's what a lot of over-the-counter cosmeceuticals try to do."
Some vehicle ingredients that can help restore the skin barrier include hyaluronic acid and dimethicone/cyclomethicone.
She gives the example that 20 percent glycolic acid in a moisturizing lotion will be less irritating than putting straight 20 percent glycolic acid solution on the skin.
"The active ingredient can affect the skin barrier function negatively by compromising the skin's natural protective layer. The vehicle can offset this potential damage enough so that the active ingredient can serve its intended purpose of reducing the appearance of wrinkles without irritating the skin. However, the choice of vehicle can sometimes reduce the potency of the active ingredient."