Science Questions

Do cool washes kill bacteria?

Sat, 14th Oct 2006

Part of the show Science of Sight, Eye Diseases and Animal Vision

Question

Peter in Godmanchester asked:

Some washing powder manufacturers are starting to recommend that we wash our clothes at 30 degrees centigrade instead of 40 degrees centigrade. I can see the energy benefits of that, but is 30 degrees hot enough to kill bacteria in the wash?

Answer

That's a really good point and there are a few things to bear in mind with this. The smells that you get on clothes aren't actually the bacteria on your clothes per se. What happens is that your body create the ideal home for bacteria to live. They live on dead skin and sweat that you squirt out onto the body's surface. They produce trace elements and chemicals and metabolites, which soak up into your clothes like blotting paper, and they're a bit whiffy. So your clothes don't necessarily smell just because they're contaminated. When you wash your clothes you wash out those substances and that's why they have a nice smell. The excellent point you've made is whether these temperatures are hot enough to neutralise any bacteria that may be on the clothing. This could be important if you're working in a hospital, I suppose. The answer is that there are a lot of detergents in washing powder and it's very alkaline as well. It can cause caustic burns if you put it on the skin. It would take some pretty hardy bugs to survive it, but some can. Things like mycobacteria that cause TB can survive in those conditions. You maybe should consider washing at higher temperatures if you think there might be bugs loitering on there.

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