Why Does Everything You Touch Leak?

Our bodies, especially our skin, are actually made of three parts: the outermost layer is your epidermis, made of dead skin cells that we shed every day and replace with new living ones, while the middle layer is a thicker layer that keeps our skin in its original condition. The innermost layer is the dermis, which is where most of the living cells are located. As part of your daily physical hygiene, it is important to keep your skin clean from all surfaces.

Dr. Mary T. Hagen, associate professor at The University of Texas Medical Branch Medical School, has written more than 100 scholarly papers on dermal biology and function. For many years she has been a consultant to dermatologists and doctors of all specialties. Dr. Hagen is a pioneer in dermal-endocrine research and has conducted more than 50 major clinical studies on the skin. In 2002, she co-authored the first international textbook on dermal science that is now widely used in medical schools and training programs worldwide. In 2004, Dr. Hagen served on the editorial board for the latest edition of the textbook Dermal Biology, published by Taylor & Francis.

The innermost layer of skin is called the stratum corneum, which is made up of the corneocytes, which are the living cells in the skin that are responsible for the structural and functional integrity of the skin. Corneocytes are part of the outermost layer of skin, the stratum spinosum, which is called the epidermis. These cells are responsible for the appearance, elasticity, water retention, and barrier function of the skin. A study in the American Journal of Clinical Pathology in 2004 was the first clinical trial to prove that the act of washing and moisturizing the skin actually restores the outermost layer of skin cells, making epidermal surface tension to the water-retaining substances in the skin stronger, more elastic, and more water-retaining. 

The innermost layer is the dermis where the majority of our cells are located. Dr. Hagen has done more than 40 studies in the past two decades on this layer of the skin and its functions. Her pioneering research with Dr. David A. Smith and Dr. Peter Hahn of the University of Massachusetts, has shown that two kinds of cells function in the skin-epidermal barrier:  the type of dermal fibroblasts, which are type 1 (which are white) and type 2 (yellow), and type 3 (black). The white and clear epithelial cells in the epidermis are called T-cells and the type 2-producing red cells are called B-cells. Dr. Hagen’s work, published in the prestigious journals Science and Nature, demonstrated that the T-cells are crucial in protecting the epidermal barrier against injury. She also discovered that when these T cells are absent in the skin, the barrier is less effective in keeping bacteria and viruses out than when they are present. 

To demonstrate this, Dr. Hagen placed dead skin cells in the dermis of volunteers and had them incubated with bacteria and viruses. She then harvested and cultured them with T-cells. She found that when these dead cells were incubated with bacteria, the T-cells were released that protected the skin from injury. To test the efficacy of using T-cells to restore epidermal barrier integrity through an external barrier moisturizer, she asked volunteers to apply a combination of oils to their bare arms and face for eight weeks. Then for nine weeks, she exposed the volunteers to a new topical moisturizer, and then again 10 weeks later. Volunteers who applied the first moisturizer only had less epidermal barrier protection than did the volunteers who applied the new moisturizer and another moisturizer. Dr. Hagen explained that the new moisturizer was able to restore barrier integrity by increasing the ratio of T-cells to B cells that are responsible for maintaining the barrier.

Since Dr. Hagen has long believed that the outermost layer of skin was the barrier’s most effective defense against infection, it was the motivation for her early clinical research on the effects of various products on the barrier functions of the skin. After a decade of extensive research, her research led to the conclusion that: