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In the early days of Truth In Aging, I learned about something called the Hayflick Limit and the notion that cells have a limited life. I speculated that if we exfoliate regularly and dramatically — I was more concerned with retinols, deep chemical peels, laser treatments and so on — we might speed up the Hayflick Limit. As my own anti-aging beauty regimen has recently — and successfully — incorporated light peels and AHAs, as well as a retinol neck cream, I decided it was time to revisit the Hayflick Limit and the impact of exfoliation. Had I been on to something, or putting two and two together and making seven? It was time to get to the truth about the Hayflick Limit.
What is the Hayflick Limit?
It all started with Leonard Hayflick, a scientist who has changed thinking on the mortality of cells. Let’s say you take a biopsy from my skin, take it to a lab and dissolve the “mortar” that holds together the cells, leaving individual cells. These cells, if “treated nicely” (as Doc Hayflick himself put it on an NPR RadioLab program), will divide and proliferate. Scientists used to assume that they would do so indefinitely until Hayflick discovered that cells are not immortal. Cells don’t just keep dividing forever, but eventually stop and then die. And how many times do they divide before dying? A mere 50-something times.
But why do they stop? This is where telomeres come in.
If DNA is broken there are two options after the cell cycle is stopped: repair or death. If cells divided without telomeres, they would lose the end of their chromosomes, and the necessary information it contains. They are often described as being like the tips on the ends of shoelaces that stop them unraveling. Telomeres shorten every time a cell divides until they shorten to a critical length. And that’s when the cell dies.
What about skin cells?
Someone once left a comment on Truth In Aging saying that skin cells don’t have a Hayflick Limit. Stem and cancer cells keep on going, but all other cells in our bodies have their 50-or so limit. An article on Beauty Brains was a useful starting point for my research into this. The short answer is that they do.
A keratinocyte is the predominant cell type in the epidermis, the outermost layer of the skin, accounting for about 90% of the cells found there. They start out from keratinocyte stem cells reside in the basal (deep) layer of the epidermis. Then they differentiate (become normal cells) and migrate to the surface of the skin. And that is where they reach their Hayflick Limit and die.
And that is why exfoliation leaves the skin looking younger and more radiant. It removes those dead cells.
But will deep exfoliation speed up the Hayflick Limit?
If exfoliation techniques are doing more than just swiping off cells that have already reached their Hayflick Limit, are we speeding up the process? Beauty Brains says not — because the stem cells in the stratum basale reproduce without limit to make more keratinocyte cells. Sounds reassuring, but unfortunately it is more complex than this. Stem cells do die. Embryonic stem cells are not subject to the Hayflick Limit, neither are cells in the muscles. Some adult stem cells may also not reach their Hayflick Limit, but science seems hazy on this. One scientific study estimates that stem cells in mice live for a few months or at most three years before shuffling off their mortal coil. So, for now, I’m not counting on a stash of invincible stem cells in my deep epidermis to keep replenishing my skin.
OK, but is exfoliation a good thing or a bad thing?
SmartSkincare.com makes a good point about cells that have reached their Hayflick Limit. They don’t always die, but hang about: “Instead they enlarge, lose their useful functions, slow down and just sit there lazily interfering with younger cells.” The skin of older people has three times “senescent” (past their sell-by date) fibroblasts as young skin. Research has shown that cells near their Hayflick Limit secrete collagenase, which breaks down collagen. Not a good thing.
So helping to clear them off the surface of the skin would seem to be a good thing, especially as we age. I am thinking that AHAs and BHAs are probably a good thing and can be used regularly, with plenty of antioxidants to go along with them. Retinol and microdermabrasion I would confine to limited use, stopping when damage has been removed and is repairing. Deep peels, laser treatments and so on that traumatize cells into dividing themselves would seem to speed up the Hayflick Limit.
In the course of my research, I found out that when cell apoptosis (death) occurs, phospholipids engulf the cell fragments, degrade the individual chromosomes and carry them out of the body as waste (source). Phospholipids also help retain moisture and, therefore, sometimes appear in anti-aging skin care. It now seems there is another reason — dead cell spring cleaning — to look out for them. Phospholipids are featured in BRAD Sublime Youth Creator Gel Cream ($245 in the shop), Apothederm Firming Serum ($75 in the shop) and in Step 2 (Step 1 will give you all those AHAs and BHAs) of Dr. Dennis Gross Medi-Spa Peel ($110 in the shop).
Can we do anything to extend the Hayflick Limit?
Hayflick himself says that cells will stop dividing and hang around indefinitely if frozen. As it’s not very practical to freeze ourselves, what else is there? L-carnosine is an amino acid that actually extends the Hayflick Limit. As mentioned above, skin cells can only reproduce themselves around 52 times, while carnosine extends this to over 60 times. Prana Reverse A ($48 in the shop) has carnosine as an intelligent counterpart to retinol.
There are some relatively new actives that work on our telomeres. One is teprenone, also known as Renovage. There's also a natural version found in astragalus. They work by stabilizing the telomeres so that they won’t shorten, and this can extend the life of the cell by one third.
Products with Renovage:
LED light therapy and ultrasound also work at the cellular level. LED increases production of ATP (the energy engine of cells) leading to increased cell proliferation and migration (particularly by fibroblasts). Ultrasound energy causes the movement of fluid waves against the cells. This may result in alterations in ion concentrations and stimulate an intracellular cascade, resulting in increased fibroblastic activity and collagen formation. Truth Vitality Lux Renew ($279 in the shop) has LED light and ultrasound.