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Soaps are 'surface active agents' (surfactants) that clean by emulsifying oil and grease, making them water soluble. Ordinary soaps are derived from animal or vegetable fat that has been treated with sodium or potassium hydroxide (caustic soda, an alkali). In hard water, soaps react to form scums of insoluble calcium and magnesium salts which may build up as residue on clothes, wash basins and pipes. In Australia, personal soaps must contain more than 70 per cent of actual soap (soluble salts of fatty acids), less than 10 per cent of 'superfatting' agents (wool-wax, fats) and less than 17 per cent water. They also contain preservatives, anti-oxidants, fragrances, and colouring matter (titanium dioxide in white soap).

Health effects
Generally, soaps are harmless but, like all cleaning agents, they remove the skin's natural oils. Soaps irritate eyes and mucous membranes, and some can irritate sensitive skins. Some people are hypersensitive to the fragrances.

Environmental effects
Soaps are more completely biodegradable than synthetic detergents and do NOT contribute to algal problems. Soaps are also more readily removed in the secondary sewage-treatment process than detergents and therefore cause fewer environmental hazards. However, the grease emulsified by the soap is liberated if sewage is pumped into the ocean after only primary treatment. It then forms 'grease balls which can rise to the surface and float onto beaches as a 'scum'.

Alternatives
Clean very sensitive skins with oil or one of the non-allergenic products. Reduce the amount of soap needed for washing by adding a small amount of a water softener like borax or washing soda (sodium carbonate). Soaps often contain animal products (e.g. tallow), however plant-based soaps are available.

 
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