How does a shampoo work?

What constitutes a good shampoo?

Caring for one’s hair is just as important as caring for one’s face, but often gets less attention. Understanding what constitutes a good shampoo is an important part of making sure your hair stays healthy and voluminous.

To help you navigate the world of hair care products, we introduce you to the basics you need to know.

How should a shampoo function? 

A shampoo is expected to cleanse the scalp and hair of dirt, sebum, sweat, dead skin cells and environmental pollutants. It also should remove greasy residues from hair care products such as oils, gels and sprays.

While most products can accomplish a thorough cleanse, the real challenge lies in removing just enough sebum to allow the hair to be clean without drying it out.

This explains why most shampoo formulations have a secondary function of smoothing the hair’s surface and imparting lustre, smoothness, buoyancy and volume.

Ingredients

Typical shampoos contain 10 to 30 ingredients. These include: cleansing agents (surfactants), conditioning agents, special care ingredients, and additives. The surfactants are responsible for cleansing hair while the conditioners and other ingredients do the rest.

Types of surfactants

A surfactant is often amphiphilic, meaning its molecules contain both lipophilic (oil-attracting) and hydrophilic (water-attracting) parts. The oil-attracting parts bind to sebum while the water-loving sites parts to water. Such a mechanism allows sebum to be removed when in contact with water.

The type of surfactants used in shampoos is classified according to their hydrophilic polar group. The four common categories of shampoo surfactants are anionics, cationics, non-ionics and amphoterics. Most formulas rely on two types of surfactants.

The surfactant listed first in a shampoo’s ingredient list denotes the primary cleanser and also the ingredient in the highest concentration. The surfactant listed second is the secondary cleanser; this is often added to offset the weaknesses of the first surfactant.

Anionic surfactants

Anionic sufactants are named for their negatively charged hydrophilic (water-loving) parts. Derived from fatty alcohols, they are good at removing sebum from the scalp. However, excessive cleansing with anionic surfactants leaves the hair harsh, rough, dull, frizzy and prone to tangling.

Cationic surfactants

In contrast to anionic surfactants, cationic sufactants have a positively charged element. Cationic surfactants are poor cleansers and do not lather well. They are also not compatible with anionic surfactants. However, they are excellent at keeping chemically damaged hair soft and manageable. As a result, shampoos for damaged or coloured hair often include cationic surfactants. Examples include long-chain amino esters, ammonioesters, and cetyltrimethylammonium chloride.

Amphoteric surfactants

With both positively and negatively charged groups, amphoteric surfactants foam well and condition the hair. In addition, they do not cause stinging in the eyes and are gentle on the skin/scalp barrier, making them ideal for mild shampoos. Examples are betaine, sulfonate betaine, amphoteric acetate/diacetate.

Nonionic surfactants

Nonionic sufactants do not have a charged group and hence are compatible with any surfactant. Nonionic surfactants are the mildest type of surfactant but lather poorly. Such surfactants are often used in baby shampoos. Examples are fatty alcohol ethoxylates, sorbitan ether esters, and alkyl polyglucosides.

Conditioners (in shampoo formulations)

Shampoo formulations tend to add hair-conditioning ingredients to impart manageability, gloss and antistatic properties to the hair. Many are noted as ‘2 in 1’ to indicate the presence of both cleansing and conditioning benefits.

Examples of conditioning ingredients are fatty substances such as vegetable oils, wax, lecithin and lanolin derivatives, protein by-products (collagen, silk, animal proteins) and silicones.

Silicones add lubricity to the hair and reduce friction that arises from combing. They make it easier to comb through and detangle strands and prevent them from becoming frizzy.

Protein substances found in conditioners function by temporarily mending split ends and holding the hair fragments together until the next shampooing takes place.

Speciality additives

To stand out in the market, certain shampoos may offer other attractive ingredients such as panthenol, pro-vitamins or botanicals such as tea tree oil. However, given that the contact time of the product with the scalp and hair is brief, it is unlikely that these provide significant clinical benefits. Such additives function more as a marketing tools.

Shampoos for special conditions

For shampoos that target conditions such as dandruff or seborrhea (oily scalp), active ingredients are added.

Dandruff is often due to the overgrowth of a yeast called Malassezia spp. Anti-dandruff shampoos rely on ingredients that can inhibit the overproduction of yeast cells. Such ingredients include zinc pyrithione, ketoconazole and selenium disulphide.

For patients with oily scalps, coal tar can be an effective ingredient in reducing sebum production.

For deep cleansing of the scalp with pharmaceutical grade ingredients, consider Deep Cleanse Shampoo. It degreases oily scalps, calms irritated or sensitive scalp problems and improves hair loss control, This shampoo also contains zinc pyrithione to target dandruff, thus suitable for many hair types.

© 2018 TWL Specialist Skin and Laser Centre. All rights reserved.

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Meet with Dr. Teo Wan Lin, an accredited dermatologist at TWL Specialist Skin & Laser Centre, for a thorough consultation to determine the most suitable treatment for your skin.

To book an appointment with Dr. Teo, call us at +65 6355 0522, or email appt@twlskin.com. Alternatively, you may fill up our contact form here.