Why do chillies stay on your hands?

Adam Murphy had look into Nancy's burning question...

Nancy - Why does chilli stay on your fingers for so long after cooking with them, even after you wash your hands multiple times it can still hurt if you touch your eyes!

Adam - Have you ever been there? You’ve had a spicy dinner and afterwards, despite having washed up, you give your eyes a rub, and suddenly there’s pain everywhere? What’s that about? Well, Tim Woodman from the University of Bath has an answer...

Tim - This is a great question. A simple answer would be that you haven’t washed your hands well enough, but of course it’s a bit more complex than that. The active component in chillies, capsaicin, is a non- polar molecule, which means it’s a lot happier interacting with oils and fats than with water. It’s also extraordinarily potent, with tiny quantities able to produce a significant effect, as you have found when you get some in your eyes.

Adam - As so many of us have found to our detriment. But why is it so hard to get rid of?

Tim - When capsaicin gets onto your hand it finds a conducive environment – the skin is quite hydrophobic (i.e. it repels water, partly due to the presence of natural oils). When you try to remove it by washing, the capsaicin prefers to stay with the oils, even when soap is used. The distribution of capsaicin between the skin and the water greatly favours the skin, so even if you repeat the washing multiple times, some still remains.

Adam - So lots of hot soapy water is called for whenever you’ve been cooking with chilli. Or gloves, as chiralSPO pointed out on the forum. That’s not the end of the chilli story though. There’s another, weirder reason.

Tim - Capsaicin is used as a pain treatment, and is delivered through the skin, from a cream formulation. Here the molecules of capsaicin are helped to pass through the layers of skin by some of the components of the formulation so that the drug can reach its targets. Its not impossible that a similar effect happens with chilli juice – some of the capsaicin not only stays on the surface of the skin, but actually enters the top layer of the skin – the epidermis. Over time this may migrate back to the surface, and hey presto, you touch your eye and find yourself in pain yet again

Adam - Thanks to Tim for answering our burning question. Next week, we’re seeking an answer to this question from Mejnun:

Mejnun - I have learned at school that when an electron excites it jumps to another orbital around the nucleus. If an electron jumps an orbital you would expect that at that moment it can be found between the two orbitals. My teacher told me that this is never the case. I can not wrap my head around it. Does the particle just disappear in one orbital and appear in the other? Is this instant, is the particle in the other orbital the same? Can you please help me to understand this?