Could your tattoos put you at risk of heat stroke?

"Do you have a tattoo? You may be at-risk of heat stroke as inked skin produces significantly less sweat than normal," the Mail Online reports.

A small US study, involving 10 men, found tattooed skin produced less sweat, which could lead to over-heating.

The drug pilocarpine was used to induce sweating on the participants' tattooed skin and then on non-inked skin on the opposite side of the body. The researchers found less sweating in the tattooed skin and the level of sodium was higher (sweat was more concentrated).

Sweat serves an important role as part of the body's "thermostat", by helping regulate the body's temperature, as it cools you off when it evaporates from your skin.

The authors suggest the possibility that high temperatures combined with a large proportion of tattooed skin would limit heat loss and so could increase risk of heat exhaustion and heatstroke. However, this has not been explored.

As a general health point – tattoos aside – if you notice someone has signs of heat exhaustion, such as tiredness, feeling faint, headache, feeling sick, or is very thirsty, you should get them to lie down in a cool place, remove unnecessary clothing, cool their skin and get them to drink fluids.

Read more advice about treating heat exhaustion.

Where did the story come from?

The study was carried out by researchers from Alma College, Michigan in the US and was funded by Alma College.

The study was published in the peer-reviewed journal Medicine & Science in Sports & Exercise and the authors declare there were no conflicts of interest.

The Mail Online reported the study accurately, saying that it is currently unknown whether long term health would be affected by the finding that tattooed skin produces less sweat. However its headline suggesting that if you have a tattoo you may be "at-risk of HEAT STROKE," (in full caps) is jumping ahead of what the study actually showed, as the effects of heat were not actually studied.

What kind of research was this?

This was an experimental study that aimed to look at differences in sweat secretion and amount of sodium in the sweat between tattooed and non-tattooed skin. It involved use of a medical device designed to induce sweating and participants were tested twice, once on their tattooed skin and once on their non-tattooed skin.

The tattooing process involves puncturing the skin with needles loaded with dye into the dermal layer. The dermal layer is made up of collagen fibres, nerves, blood vessels and glands, including sweat glands that produce sweat when the body heats up and exceeds regular temperature levels.

Researchers wanted to see if the tattooing process impaired the function of the sweat glands, and if so, by how much.

This study is useful to look into this as it is analysing skin from the same person twice and therefore everything other than the tattooed/non-tattooed skin remains the same. However, the extremely small sample size and lack of any further investigation into potential effects on body temperature make it quite limited.

What did the research involve?

Researchers took 10 healthy males who had a tattoo on one side of their body, and compared their sweat rates and the level of sodium in their sweat to the same (non-tattooed) area on the other side of their body.

The tattoos were on the upper back, shoulder, upper body, upper arm or lower arm and completely covered a circular area of at least 5.2cm2. The patch of skin with the highest density of ink was used as the tattooed area. The unmarked skin in the exact opposite position on the other side of their body represented the non-tattooed skin.

Sweat was induced using gel disks containing pilocarpine, a substance used to induce sweating. The disks were attached to electrodes that were used to deliver pilocarpine into the skin in two five minute sessions.

After the second session, sweat was drawn into tubing that was modified to allow sweat collection into a disk. The sweat rate was measured by looking at the change in weight of the collection disk before and after sweat collection.

Sweat was then diluted and the sodium concentration of each sample was measured.

Sweat rate and sodium concentration were compared for the tattooed and non-tattooed skin of each participant.

What were the basic results?

• All 10 participants generated less sweat from tattooed skin than non-tattooed skin.
• The mean ratio of sweat rates from tattooed to non-tattooed skin was 0.53 (±0.12), therefore the average sweat rate from tattooed skin was about half the sweat rate from non-tattooed skin.
• Nine of 10 participants had higher sodium concentration in their sweat from tattooed skin than non-tattooed skin.
• The mean sodium concentration from tattooed skin was 1.73 times higher than non-tattooed skin.
• Age of tattoo did not seem to have an effect.

How did the researchers interpret the results?

The researchers conclude that tattooed skin has a lower sweat rate and a higher sweat sodium concentration than non-tattooed skin. They say: "Additional studies need to be conducted to determine the mechanism associated with these changes in sweat function and the extent that they may affect thermal balance."

Conclusion

The study showed that artificially stimulating sweat glands in a tattooed area of skin in 10 men produced a lower sweat rate than stimulating sweat glands in a non-tattooed area of skin in the same person.

The authors suggest a number of possible explanations for this, including that it may be because tattooing skin starts an inflammatory response that may cause damage to normal tissue including sweat glands. However, these are only theories and need to be investigated further.

While this is interesting preliminary research, there are some important things to remember:

• There were only 10 male participants involved in the study. A much larger study would be needed to see if the findings still hold true.
• 7 out of 10 participants had their tattooed skin tested first. This might have had an effect on their sweat rate, for example if their body continued producing sweat from the first round and this was included when their non-tattooed skin was later tested.
• The sweat glands were artificially stimulated in an environment where the level of heat was kept constant. We don't know if this represents the sweat response caused by over-heating in the real-life situation. We certainly don't know whether it could have effects in terms of making you more likely to over-heat and develop heat exhaustion or heat stroke, as with the media's rather bold assumption.

In any case, even if tattoos do impair sweating, the odd couple of tattoos scattered on your skin are unlikely to have much of an effect on your temperature regulation. It could be more of an issue if you had large portions of your body covered with tattoos. But even then as said, this tiny study proves little and the findings need confirmation.

The Mail's reporting of the study, slightly over-hyped as it was, highlights the fact that all of us should be aware of the signs of heat exhaustion and the subsequent steps – get the person to lie down in a cool place, cool their skin remove unnecessary clothing, and get them to drink fluids – that should be taken.