There are a plethora of active ingredients that have been shown to affect skin behavior by, for example, stimulating collagen and elastin, suppressing melanocytes and reversing glycation. Yet, no matter how well a hot new skin care ingredient performs in vitro or on porcine skin samples in a lab, it is only of value to consumers if it can safely penetrate human skin to reach its targets in living tissues and cells. Blocking the path is the skin barrier, as the name implies.
“The keratinocytes go through a process (called keratinization) whereby they become elongated, lose their nucleus and wind up as the top layer of dead skin cells. That is our barrier,” explains John Kulesza, formulation chemist and president of Young Pharmaceuticals. “A barrier we need to overcome if we wish to deliver topical agents.”
Actives can reach their targets beneath the stratum corneum via physical efforts (by washing or scrubbing to remove dead cells), using permeation enhancers or a combination of both. Choosing the correct delivery method depends on the characteristics of the ingredient and the target you are trying to reach.
Reaching the Right Targets
How deeply you want an active to go in the skin depends on the goal of that active ingredient, says Joshua Zeichner, MD, associate professor of dermatology and director of cosmetic and clinical research at Mount Sinai Hospital in New York City. In other words, it’s less about how deeply and powerfully an active can penetrate and more about whether it can reach its precise destination.
“For moisturizers, the goal is to improve hydration in the epidermis. Most skin pigmentation deposits in the epidermis, or the outer skin layer,” he says. “Issues such as acne and aging skin, [on the other hand] occur at the level of the dermis, or lower skin layers. This is where oil glands become blocked. The dermis is the part of the skin where collagen and elastic fibers provide structure and support of the skin as well.”
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Virginia Pelley is a freelance writer based in Tampa, FL.