So here we go,
I managed to get some insect repellent (DEET) on my helmet and it was a bit sticky so decided to clean it. Warm soapy water wasnt doing the trick so I thought I’d try non-antiperspirent deoderant (a trick for cleaning racing helmets due to the alcohol content).
Whats resulted can be seen in the pictures.
I doesn’t seem to be a precipitate but I can’t tell whether its just a reaction with the deet that I still can’t get of the helmet or if the helmet has essentially been chemically etched by the combination.

Any ideas how to sort it?

[/url]20160620_195736 by joespencer_33, on Flickr[/img]

Yes, that’ll be deet dissolving your helmet. Nasty stuff, try finding something with IR3535 or (p)icaridin in instead.

Looks like something deet would do. Unfortunately there isn’t a thing you can do to remove the mark. Maybe paint over it.
Deet is awful stuff melts plastic easily, did any get onto the foam of the helmet as you might want to check it closely

DEET is well known for attacking plastics. As a climber, I make sure the stuff never gets near ropes, draws and slings. Never tried it near my bike helmet, never will having seen yours. Bin it and treat yourself to a new one.

It’s not a sticky residue from the insect repellent – it’s partially dissolved plastic. Into the bin!

DEET is famously bad news for plastic. Have you been living under a rock for the last 70 years?

No need to be like that Scienceofficer – Obviously I wasn’t aware otherwise I wouldn’t have done it and cost myself £100

Sorry, I was only teasing.

DEET pretty much melted my Swatch watch as a kid 🙁

If it’s only on the polycarbonate shell it’s cosmetic not structural. Ugly but no less effective. If it’s got into the polystyrene then I’d bin it.