How does anti-dandruff shampoo work? Dandruff is caused by overgrowth of yeasts such as pityrosporum ovale which live on normal skin. The overgrowth causes local irritation, resulting in hyperproliferation of the cells (keratinocytes) forming the outer layer of the skin. These form scales which accumulate and are shed as dandruff flakes. Anti-dandruff shampoo works by three mechanisms. Ingredients such as coal tar are anti-keratostatic and they inhibit keratinocyte cell division. Detergents in the shampoo are keratolytic - they break up accumulation of scale. Also, anti-fungal agents such as ketoconazole inhibit growth of the yeast itself. Other components such as selenium sulphide also inhibit yeast growth and, therefore, scaling. Why do we get a dry throat when we are nervous? When we are nervous, the body is set into the 'fight or flight' state. This is caused by an activation of the autonomic nervous system. It is seen throughout the animal kingdom, and has evolved to help the animal deal with dangerous situations, such as escaping from predators. The nerves are selectively activated, depending on how important they are for the response. Because eating is not considered important at this time, the nerves to your mouth that control your salivary glands are suppressed, so your mouth dries up. In addition, your pupils dilate and the blood vessels to your heart and muscles are enlarged in order to get the blood to the most important organs needed for whatever drastic action is necessary. How do chameleons change colour? Chameleons' special skills make them very effective predators. As a chameleon lies in wait for prey, its skin changes colour to blend with the surroundings. Chameleons have two layers of cells with red and yellow pigments called chromatophores under their top transparent layer of skin. Under the chromatophores are other layers that reflect blue and white light. Further down is the brown chemical melanin, which causes skin to tan in humans. Excitement, anger, or bright light causes the colour cells to enlarge or contract, transmitting a spectrum of colours appropriate to the occasion. When a chameleon is calm, it turns green by partially blocking the blue-reflecting layer with yellow pigment. When it is angry, yellow totally blocks out the blue layer underneath. The colours chameleons can turn include brown, yellow, reddish brown, black and white. Graphic: SPBRAIGLO
