Why avoiding the sun every other day is key to a perfect tan

Sunbathing on consecutive days disrupts natural cycle of the body and stops you going brown, say scientists

HOLIDAYMAKERS hoping for an impressive tan should only sunbathe on alternate days, a study suggests.

Researchers at Tel Aviv University in Israel have found that the pigmentation process that protects the skin from damaging ultraviolet rays works on a 48-hour cycle.

If people sunbathe daily, the full sequence does not have time to run and so a tan takes longer to build.

The scientists found that skin cells exposed to UV rays daily developed around half the tan of those exposed every two days.

Enjoying the sun every other day also halved the exposure to radiation which could cause skin cancer, while allowing the body to complete its defence cycle and repair damage.

“The damaging effects of high doses of ultraviolet rays are known, but we were curious to see the effect of exposure frequency on skin,” said senior author Dr Carmit Levy, a molecular geneticist.

“It turns out that if you are going out daily to the beach, you might be interfering with the natural scheduling and synchronising of the skin-protection systems.”

The skin first responds to sunlight by creating an immune response which repairs damage and builds a thicker layer of cells to protect more delicate layers beneath. It then produces melanin, a browny-black pigment present in skin, eyes and hair that tans the skin and acts as a sunscreen.

The immune response begins within seconds of exposure to sunlight, but the melanin phase can take hours or even days to start.

To understand the exact timings, the team exposed human skin cells and mice to ultraviolet light daily, every other day or every three days, and measured the amounts of melanin which were produced.

They observed that a 48-hour cycle resulted in the darkest colouration of cells, and minimised damage. They believe that the 48-hour cycle may have arisen after our ancestors lost their fur, but are not sure why.

“The results were so surprising,” added Dr Levy.

“We expected daily synchronisation of the cell’s protective cycles.

“We’re not sure why we would have evolved for a 48-hour cycle when ancient humans were probably exposed to the sun every day

“We do know that vitamin D, which the skin produces upon exposure to the sun, is stable in the blood for 48 hours post-exposure. Perhaps there is a link.”

The team also found that the cycle was driven by a chemical known as microphthalmia-associated transcription factor, or MITF, which fluctuates on a 48-hour cycle.

However, exposure to sunlight on a daily basis upsets the cycle of the chemical, knocking it out of its natural rhythm.

The research was published in the journal Molecular Cell.