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Tanning lotions and fake tans are considered a safer alternative to sitting out in the sun for hours - but how exactly do they work?

According to chemistry teacher Andy Brunning, the reaction they create with our skin is the same reaction that occurs when browning meat in a hot pan.

Mr Brunning has created an infographic to explain how chemicals in the lotion react to skin cells, and why this causes the skin to turn brown.  

An infographic (pictured) created by chemistry teacher Andy Brunning shows that tanning lotions contain dihydroxyacetone, commonly abbreviated to DHA, and erythrulose. Tanning lotions contain up to 15% DHA, but many sit within the three to five per cent range. The higher the percentage, the darker the tan

'We're all well versed in the dangers of spending too much time in the sun,' said Mr Brunning on his blog Compound Interest. 

HOW DO TANNING LOTIONS WORK?

Tanning lotions take around two to four hours to take effect, and will continue for up to 72 hours

DHA reacts with amino acids in dead skin cells to produce chemicals called melanoidins.

This is known as a Maillard reaction, which is also the name given to the reaction that causes meat to brown when cooked.

These melanoidins absorb certain wavelengths of light, and this results in them appearing brown on the skin.

This reaction takes around two to four hours to take effect, and will continued for up to 72 hours.

As the dead skin cells are shed, these colour fades and this cycles takes around 10 days. 

'However, if you're unlucky enough not to have the time for a couple of weeks on the beach, you might be tempted to resort to tanning lotions to achieve a tanned look.'

'These can induce the appearance of a tan, through the action of the chemicals they contain.'

Mr Brunning continued that the main chemicals used in tanning lotions are dihydroxyacetone, commonly abbreviated to DHA, and erythrulose.

DHA can be used on its own, and while erythrulose produces a more gradual effect, and is often used with DHA, it is rarely used on its own.

Tanning lotions contain up to 15 per cent DHA, but many sit within the three to five per cent range. 

The higher the percentage, the darker the tan.

DHA reacts with amino acids in dead skin cells to produce chemicals called melanoidins.

This is known as a Maillard reaction, and is also the name given to the reaction that causes meat to brown when cooked.

These melanoidins absorb certain wavelengths of light, and this results in them appearing brown on the skin.

Brunning continued that studies have previously found the amount of UV-induced free radicals - oxygen molecules said to have a hand in everything from ageing to diabetes and cancer - produced 24 hours after lotion was applied is 180 per cent higher than untreated skin.

DHA reacts with amino acids in dead skin cells to produce chemicals called melanoidins. This is known as a Maillard reaction, which is also the name given to the reaction that causes meat to brown when cooked. These melanoidins absorb certain wavelengths of light, and this results in them appearing brown on the skin

Put more simply, this means the skin is more sensitive to UV rays a day after application and should be protected. 

Other studies have found that DHA from tanning lotions is absorbed by living skin tissue – as much as 11 per cent, but it's unclear if this has any effect on the body.

Elsewhere, normal tanning is created by melanin produced in the skin. 

When people use fake tan, they may believe they have developed natural protection from the sun's rays, added Mr Brunning, meaning that many don't use extra protection, and put themselves at risk.

He continued that tanning lotions have an SPF rating of three, on average.