Shampoo: Encyclopedia II - Shampoo - Description

Shampoo - Description

Shampoos are used to clean hair by stripping sebum from the hair. Sebum is naturally occurring oil that coats the hair and tends to collect dirt, styling products and scalp flakes. Surfactants clean hair by stripping sebum from hair shafts therefore removing the dirt attached to it.

While both soaps and shampoos contain the cleaning agent surfactants, soap is specifically designed to clean the body and might be too harsh on hair.

The difference between shampoo and soap include:

• Proper detergency without degreasing
• Ability to form delicate and rich bubbling
• Easy rinsing
• Good finish after washing hair
• Minimal skin/eye irritation
• No damage to hair
• Low toxicity
• Good biodegradability

The chemical mechanisms that underlie hair cleansing are complex. Undamaged hair has a hydrophobic surface to which skin lipids are strongly consumed. The skin lipids (sebum) are so strongly attached to hair that they will not come off with plain water. When shampoo is applied to wet hair, the anionic surfactants are adsorbed onto the hair shaft by their hydrophobic tails and the negatively charged heads orientate outwards. The hair fiber's surface is then wetted by water that has had its interfacial tension reduced by the surfactants. This displaces any non-polar materials (oil, grease) that are attached to the hair shaft. The semi-polar oily materials also on the hair shaft are solubilised into the surfactant micelle structures of the shampoo and are removed by rinsing. Particulate matter adheres to hair primarily due to adhering to the oily surface, and are easily removed by rinsing once the oil is solubilised into the shampoo.

Adapted from the Wikipedia article "Description", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki