One hot day, back in the summer, I noticed that the front of my thighs were sore. Nothing awful but there was a pronounced tenderness in the region of my quadriceps muscles as I moved around. At first I didn't think anything of it but the discomfort increased. Twenty four hours later, both my legs were quite painful and eventually, when I could no longer ignore the problem, I pulled down my trousers to examine the tender spots. What I saw was quite horrifying. The skin above my knees on both legs was vividly red and blotchy. Several blisters were evident: the left side was particularly bad. At first I was mystified about the pathogenesis of these lesions (see Picture #1 below). I cogitated on the matter for a bit. Was it some strange bacterial infection? A Staph perhaps or worse some horrendous, flesh-eating, bug (technically necrotizing fascitis caused by a Group A Streptococcus)? Possibly it was an incipient autoimmune condition such as pemphigus or even a T cell lymphoma. I felt distinctly neurotic as my imagination ran riot. Sometimes it doesn't help to have a background in immunology/microbiology. And then the light bulb went on...! The previous day(s) I'd done quite a bit of work on my laptop with the machine on my, err, lap. Generally I try to work with it placed on a desk as I'm very aware that extensive typing with a computer placed on one's knees leads can lead to postural problems (I have the chiropractor's bills to prove it). However for a number of reasons I'd been using the machine on my lap on this occasion. The computer in question is a 2011, metal-cased, MaBook Pro with a 15" screen. It's quite powerful and its heart (or should I say brain?) comprises four Intel microprocessors clocked at 2.2GHz. All this grunt comes at the price of power consumption and heat is produced as a consequence. I'd noticed that the bottom of the Mac became quite warm after use. But could it have been burning my skin without me noticing? I'd never had any problems with laptops in the past although they were invariably plastic case models and did not have the conductive problems of aluminum. Furthermore I'd never owned a machine as powerful as my MacBook Pro.
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1. Author's left thigh above the knee. Large florid blotchy patches and blistering that occurred after laptop use. The right leg was slightly less affected.
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2. The temperature almost anywhere on the rear of the case exceeded 110°F. |
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| 3. Around the rear left of the case, directly below the microprocessor cluster, the temperature approached and exceeded 120°F within a few minutes. |
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| 4. Another temperature reading after being revved up for 3 minutes with YouTube usage or the video game "Rage". 120°F was achieved very easily and more intense provocation would probably generate temperatures in excess of those recorded here. |
I fiddled around with the machine, deliberately trying to make it work hard by giving it demanding jobs such as playing big videos from YouTube and running various games. It did seem to get pretty hot. but was it enough to burn skin? I had to be more objective so I purchased a small thermal scanner, revved up the Mac again and took some readings. The results were surprising. The temperature at the bottom rear of the case was always well in excess of 100°F and went up to a peak of 120°F around the rear left side of the case, exactly below the microprocessor cluster (see photos). The ambient temperature was 72°F (sorry for the use of Imperial units but the US is locked into it and regards the metric system with suspicion -if my little scanner had a built in Celsius readout, I couldn't find it). Although I repeated the procedure a couple of times, I concede it wasn't a very scientific study but if anything the readings were conservative. One thing is clear, however: the Mac gets bloody hot with just fair use and the heat is conducted very efficiently through the metal case. The Burn Foundation states that a temperature of 133°F for 15 seconds will cause third degree burns so I'm pretty sure that a piece of metal heated to 120°F+ will cause tissue damage when pressed against skin for 60 minutes or more. I was wearing trousers when the injury occurred but thy were just light, summer weight, cotton chinos which didn't provide much in the way of insulation. Why didn't I feel the burn occurring? Well, in retrospect I did notice that the Mac was disagreeably warm and I moved it about a bit to mitigate the discomfort but at no time did I suspect it was causing a burn of any kind.
Anyway that's the story. Two, no three, months later my skin is still quite red and blotchy and I think will take the rest of the year to fully heal. I did mention the incident to a resident Genius in the local Apple Store and he pointed out that MacBooks aren't meant to be used on a lap even though they are universally termed "laptops". There's an irony in this somewhere. Let the user beware: you have been warned! P.S. Note added two weeks after the initial post: I've just learned that my condition is a well documented phenomenon and is known as erythema ab igne or toasted skin syndrome. How I hate hindsight...!
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