The Science of Colour 3

How coloured compounds have been impotant in medicine
07 January 2007

Interview with 

Colour in headache cures, and treating disease - Anna Lacey


Chris - It's time now for the third part in our series on science and colour, and this week Naked Scientist Anna Lacey has been looking at how colour plays a crucial role in medicine and in the pharmaceutical industry.

Anna - I'm lucky not to get headaches that often, that is, unless I've had a beer or three too many… But for the people I asked here at Addenbrooke's hospital, there seems to be a universal cause for headaches. Stress! But regardless of whether the cause is stress or alcohol, what is it that's going on at the microscopic level when we have a headache or feel pain? Here's Dr Michael Randall from the University of Nottingham's Medical School.

Michael - We have pain receptors in the body, which can be stimulated by a chemical family called prostaglandins. And one action they have is that they sensitise those pain receptors and make them more sensitive to pain. So the body is aware of pain and inflammation.

Anna - So in order to get rid of pain, we need to get rid of these prostaglandins. But how can we do that? Well you might not have realised it, but every time you take a drug like paracetamol or aspirin, you're actually stopping the production of prostaglandins. Aspirin, for instance, locks onto the molecule that makes prostaglandin in the first place - and if you stop prostaglandin production, then you stop the pain. But what's this got to do with the science of colour? Well last time I talked about how coal tar gave rise to the colour mauve, which was the very first synthetic dye. Now it turns out that chemicals derived from coal tar were also used in the development of aspirin and paracetamol - so bizarrely both our high streets shops AND medicine cabinets have benefited from the same black goo. Now that all happened in the 19th and early 20th century, but colour's still vital in cutting edge treatments even today - and one of these is called photodynamic therapy. So what's that all about? Here's Professor Stan Brown, the director of the Centre for Photobiology and Photodynamic Therapy at the University of Leeds.

Stan - Photodynamic therapy is a newly developing approach for the treatment of a variety of diseases including cancer and infectious diseases, which uses a coloured drug that in itself is harmless, but is activated when you shine light on it. When the drug is in the target, which could be a tumour or a bacterial cell for example, we shine the light on to the target. The drug, or the photosensitiser as we sometimes call it, then absorbs the light and takes in the energy from that light. That energy is then passed on to ordinary molecular oxygen, which is everywhere, including inside the body. The trick is that this energy then converts the oxygen into a very activated form, which destroys the cells immediately around it, but no further than that.

Anna - So what colour are these photosensitising dyes?

Stan - Ideally we try to have blue dyes. They're usually a beautiful colour of blue, so it's quite an interesting area to work in for clinicians as well as scientists. They're blue because they absorb red light, and the reason we use red light is that it penetrates into the tissue much more deeply than other colours of light. An example of that that I always point out is that if you point a torch through your hand, it comes out red. That's not the colour of blood as we always used to think, but it's because all of the colours except red are absorbed while red penetrates and comes out the other side. So that shows why we use red light, and therefore why we use blue drugs.

Anna - Photodynamic therapy, or PDT, is proving to be very successful in the treatment of macular degeneration and in the future, is likely to be developed further for cancers and killing off superbugs like MRSA. If you want to hear more about photodynamic therapy, then you can go to our website -, to hear the full-length interview. Well if that dose of colour science wasn't enough, you can join me next week when I'll be looking at why wearing red will win you running races and how colour affects our mood.


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