Exfoliation and the Hayflick Limit
Question: Is it true that too much exfoliation can make you ‘run out of skin’ due to the Hayflick limit?
The Hayflick limit predicts that some cells have a finite ability to regenerate--up to 50 times before they die off. It is important to remember that the Hayflick limit applies only to differentiated cells, such as keratinocytes and their final stage, corneocytes, which are cells that have matured to fulfill their final function. It does not apply to stem cells which are not differentiated to meet a specific function. Epidermal stem cells—unaffected by the Hayflick limit—will regenerate for the life of the organism, continuing to differentiate into corneocytes when signaled to do so. Removal of corneocytes by exfoliation is one of those signals.
Thus the real question is: If the Hayflick limit applies only to differentiated cells such as keratinocytes and corneocytes, then why isn’t there is a limit to the number of times these cells regenerate? And if this limit is reached, will exfoliation thin rather than replenish the skin?
Answer: Even though it may seem logical to conclude that if corneocytes, differentiated cells removed upon exfoliation, are subject to the Hayflick limit, then exfoliation will thin the skin. However, this conclusion ignores the unique feature of keratinocytes---they do not regenerate. They are designed to die off cyclically, about every 35 days, a cycle which slows down with aging. Exfoliation speeds up that cycle by the removal of corneocytes, signaling the formation of newer replacements. Thus, a new layer of younger, healthier skin emerges. If this were not so, then there would be a limit to our body’s ability to heal wounds by regenerating new cells and the corneocytes that protect them.
Bottom line: Corneocytes are not affected by the Hayflick limit because they have already reached their regenerative limit. Once they are removed by exfoliation or slough off naturally, they are replaced by new corneocytes that have emerged from the epidermal stem cells, which are not affected by the Hayflick limit. Thus, exfoliate frequently---even daily depending on the method. It will not cause you to ‘run out of skin.’
Susan Nathan, LE, B.S. Microbiology
I invite questions concerning this article.