Maximum pigmentation when the cells of the skin are exposed to the sun every 48 hours

A study conducted by researchers at Tel Aviv University found that skin cells exposed to the sun reacted by producing pigmentation on a 48-hour cycle.

Image Credit: Victor Josan / Shutterstock

As recently reported in the newspaper Molecular cellExposing mice and human skin cells to ultraviolet light every other day resulted in darker pigmentation and less radiation damage than exposing the cells daily.

"The harmful effects of high doses of ultraviolet rays are known, but we were curious to see the effect of the frequency of exposure on the skin", said senior author Carmit Levy.

When exposed to ultraviolet light, the skin has a double response.

First, it induces an immune response, repairs the breakdown of DNA and generates more cells to protect the underlying skin layers.

Secondly, melanin pigments the skin and provides a natural sunscreen in anticipation of subsequent exposure.

Levy and his team wanted to know how the timing of these two protection programs was synchronized.

After exposing the mice to ultraviolet light daily, every other day, and every third day, they measured melanin production and the amount of DNA breakage.

The team found that cell exposure on a 48-hour cycle produced the darkest pigmentation while minimizing the effects of stress.

The results were so surprising. We expected a daily synchronization of cell protection cycles … It turns out that, if you go to the beach every day, you risk interfering with the natural planning and synchronization of the systems. skin protection.

Carmit Levy, lead author

The researchers also observed that MITF (transcription factor associated with microphthalmia) appeared to be involved in system synchronization. When the skin cells were exposed to ultraviolet light once, the expression of MITF fluctuated every 48 hours, while a second exposure a day later seemed to disrupt that expression.

Next, the team evaluated pigment production in human cells by directly stimulating MITF activity.

This revealed that a 48-hour stimulation cycle resulted in the most pigmentation, while minimizing stress-induced cell proliferation.

We do not know why we would have evolved during a 48-hour cycle, while older humans were probably exposed to the sun every day. We know that vitamin D, produced by the skin when exposed to the sun, remains stable in the blood for 48 hours after exposure. Maybe there is a link. "

Carmit Levy, lead author

Researchers believe that understanding the dynamics of transcription factors could provide important information to ensure that skin cancer treatments are properly timed, as it has been previously shown that some treatments depend on frequency.

Further studies are needed to replicate the results in humans before they can draw conclusions about their therapeutic potential or even how to ensure safer tanning activities.