PICTURE THIS: The ‘fishnet’ rash you get from a laptop

In a new series, we bring you fascinating pictures shared by doctors — and the stories behind them. THE pattern is so defined it could almost have been stencilled on.

But the neat red-and-white marks on this woman’s skin are in fact a form of heat rash.

Known as Erythema ab igne — the Latin for ‘redness from fire’, or toasted skin syndrome — this fishnet pattern is caused by prolonged exposure to heat.

The image was posted on Figure 1, a website where healthcare staff worldwide share medical images, and also canvass colleagues’ opinions.

In this case, the rash was the result of the patient’s arm being soaked in hot water for

20 minutes by medics to help draw out a suspected abscess.

The hot water caused the mottled rash, but experts say heat pads, hot water bottles, open and electric fires, laptops and even heated car seats can also cause the reaction.

‘ Erythema ab igne was traditionally something that affected elderly people who sat by the fire for too long,’ says Dr Tony Bewley, a consultant dermatol-

ogist at Whipps Cross University Hospital and Barts Health NHS Trust.

In Scotland, where it used to be particularly common due to the cold weather — and the need for a warm fire — it was known as Granny’s tartan, Tinker’s tartan or old ladies’ shin.

‘It occurs at any temperature that’s tolerable to the skin and won’t scald you,’ says Dr Bewley. ‘For example, it’s common to see it in people who use hot water bottles for back pain and also after a hot bath.’

These days it is often laptops, or specifically their batteries, which can reach temperatures of 44c, that cause the rash, according to a study in the journal Pediatrics in 2010.

‘Putting the computer on the lap may also block the ventilation fan, increasing the heat even more,’ said the research- ers, from the University Hospital of Basel, Switzerland.

‘What happens is that heat causes persistent dilation of the capillaries, which then leads to the leaking of a pigment from cells near the skin’s surface,’ says Dr Bewley.

While it is not usually serious, repeated reactions can make the skin and underlying tissue thinner and create lesions, causing pain and itchiness.

There is also a small risk of a skin cancer called squamous cell carcinoma (squamous cells are in the outer layer of the skin) developing in the long term, if the skin is repeatedly and permanently damaged. Heat has the same effect as being chronically sunburned.