True Facts

Short articles explaining how chemistry underpins much that we take for granted.

Oct 212011

Saliva is a cocktail of natural chemicals

The average healthy person secretes half a litre (500 mls) of saliva a day into their mouth from six glands. When we are at rest the rate of saliva production falls to around 0.3 ml per minute but when we start chewing something it then rises to 5 ml per minute . As we continue to chew it slowly falls and after about 20 minutes it will be around half this rate.

Of course the vast majority of saliva is water (99.5% in fact). However, the other 0.5% is a mixture of soluble chemicals which play a key role in providing enzymes to help us digest our food. And not only does saliva do this, it also keeps our mouth and teeth in good condition.

The chemicals in saliva are various organic molecules, inorganic ions, and large organic molecules including proteins.

The organic molecules are urea, amino acids, fatty acids, uric acid, lactate and glucose and they come from the body’s plasma so they vary according to amounts in that fluid.

The inorganic ions are chloride (Cl-), potassium (K+), sodium (Na+), phosphate PO43-), bicarbonate (HCO3-), calcium (Ca2+), and magnesium (Mg2+). The calcium and phosphate are needed to keeping the teeth in good condition because tooth enamel is a type of calcium phosphate, and saliva can help repair the teeth. The pH of saliva is 7, in other words it is neutral, and this helps to promote re-mineralisation of the tooth enamel. It is only when the pH falls below 5.5 that slight demineralisation occurs.

The large molecules in saliva are proteins, glycoproteins, antibodies, lipids and enzymes. The last of these are amylase, peroxidase, and lysozyme. Lysozyme also acts as an antibacterial agent which is why licking wounds can keep them clean of infection. The number of proteins identified in saliva has increased to around 50 and some of their functions are still unknown.

The inability to produce enough saliva is known as xerostomia and is a symptom of some conditions, including being a side effect of some drugs. Chewing gum is an ideal remedy to stimulate more saliva production.

Oct 102011

Lipsticks as we now know them first appeared in 1915 and were manufactured by Maurice Levy in the USA. They had many faults. They were not indelible, in other words they leave tell-tale traces on cups, cheeks, and collars. They melted in hot weather, and broke on cold days. And they could easily go rancid, based as they were on natural fats and colouring agents.

Cosmetic chemists eventually solved all these problems, and now there are ranges of lipsticks of many shades and textures.

The main component of a lipstick is a mixture of oil and wax chosen so that together they provide a soft texture when being applied yet remaining firm within the cartridge case. Various oils have been used, including olive oil and cocoa butter, but today the most likely natural oil is castor oil, which also has the added advantage of forming a tough, shiny film when it dries after application. Almost half the weight of some brands of lipstick is purified castor oil. An alternative to castor oil is mineral oil produced by the chemical industry which is colourless, odourless, non-toxic and non-greasy.

Wax is needed to give lipstick its shape, and typical waxes are beeswax or carnauba wax. Beeswax is the preferred one, and this melts at 63°C. Carnauba wax comes from the leaves of the South American pine and it melts at around 80°C.

Colour is usually provided by red dyes such as 4′,5′-dibromofluorescein, which is intensely red, and 2′,4′,5′,7′-tetrabromofluroescein which has a slightly purple tinge. These are combined with aluminium oxide, and the final colour that the dye takes on the lipe is partly determined by its chemical reaction with the protein of the skin. This binds the dye, thereby making it indelible, and deepening the colour slightly.

White titanium dioxide is present in lipstick for the same reason that it is added to paints, because of its superb covering ability. In the case of lipstick the whiteness of titanium dioxide serves to dilute the colour of the dyes to give shades of pink.

The addition of tiny spherical particles, known as microspheres, can also improve the texture. These tiny spheres are made of the polymer polymethylmethacrylate, which encapsulates and slowly releases other ingredients such as vitamin E and folic acid, which are said to improve the skin.

Glossy lipstick relies on lanolin for the desired effect. Pearlized lipsticks include boron nitride to impart a shimmer and lustre to the lips. (Some include micra particles to impart an extra shimmer.) Matte lipsticks have more wax and pigment, giving them more texture and less shine. Long-lasting lipstick usually includes silicone oil which helps seal the colour.

Lipstick chemistry has come a long way in the past hundred years. It is now seen as an essential part of a woman’s attractiveness, and maybe leading to another type of chemistry: sexual attraction.