What is a shampoo?
A shampoos is a cleanser designed to clean hair and scalp. Most shampoos clean hair very well. Where they differ is how the hair feels afterward, depending partly on the strength of the surfactants.
- Stronger clarifying shampoo should not be used more than once or twice a week.
- Those designed for daily use contain mild surfactants and are less likely to irritate the scalp.
Ingredients of shampoo
All shampoos are 80–90% water, 2–8% detergents and foaming agents, and about 1% fragrance and preservatives.
- Shampoos often contain antistatic and detangling agents as well as thickeners, humectants, sequestering agents, colour and conditioners.
- Effective detergents include sodium lauryl sulphate, laureth sulphate and sulfosuccinate. These are foaming agents and give the hair a squeaky clean feel.
- Clarifying shampoo contains heavy-duty surfactants. Body-building shampoo contains proteins that bond to hair and increase its volume.
Moisturizing shampoos are the best choice for dry, flyaway hair. They can cut down on static, make split ends look better (by gluing them together with proteins), and pull moisture onto hair to keep it from getting too dry.
- Revitalising or replenishing shampoos are made for colour-treated, permed, and damaged hair and contain gentler surfactants. They may include ingredients designed to retain colour or to help to repair split ends, but there's little evidence that they are effective.
- 2-in-1 shampoos with conditioner save time but may leave hair feeling dry and sticky.
- Baby shampoos contain amphoterics and have less detergent. They are not designed for cleaning adult hair, especially when styling products have been used. They may be appropriate for damaged hair and when standard shampoos cause dermatitis.
How to use shampoo
Wet the scalp and hair using warm or cool water (hot water can be drying to the hair and scalp).
- Apply a 5–10 cent amount of shampoo to palm and rub hands together to evenly distribute.
- Apply the shampoo to the scalp.
- Massage gently for about 30 seconds to form lather
- Rinse thoroughly.
Lather is destroyed by sebum so an oily scalp may require a second shampoo. Excessive lather is wasteful: it doesn't clean hair any better. Shampoo should be easy to rinse off, but conditioner, styling products and chemical processes may leave a residue.
Conditioners are designed to counteract the effect of detergents, repair static electricity and split ends. A silicone film smoothes cuticles and reduces friction and hair breakage, and maintains colour. Conditioners often contain anionics for softness and manageability.
- After rinsing off the shampoo, apply conditioner in one hand and rub palms together to evenly distribute.
- Apply conditioner from the middle of the hair shaft down to ends. Avoid the scalp unless scalp is dry.
- Comb conditioner through hair to distribute product evenly.
- Leave conditioner on hair for a few seconds to help smooth the cuticle.
- Rinse thoroughly.
Medicated shampoo may contain salicylic acid to loosen flakes of skin, and selenium sulfide, zinc pyrithione, ketoconazole or ciclopirox to reduce the numbers of Malassezia yeasts on the scalp and are used to treat dandruff and seborrhoeic dermatitis. They may also help treat scalp psoriasis and atopic dermatitis, but often shampoos containg coal tar are more useful in these conditions.
Medicated shampoo needs to be left on the scalp for longer than normal shampoo. Ideally, wet the hair 10 minutes before a shower or bath. Apply medicated shampoo as above. and massage gently into the scalp. Leave for 10 minutes and rinse off well. Follow with conditioner if desired.
Skin problems due to shampoo
Shampoos can irritate and cause scalp problems. These are rare with modern products made by reputable manufacturers if they have been designed for sensitive skin and are used appropriately. Overwashing may have the following effects:
- The pH of the skin surface may change: look for pH-balanced shampoo.
- The number and type of bacteria and yeasts on the skin surface may change, resulting in dandruff or seborrhoeic dermatitis.
- The surface oil film (sebum) is removed, allowing greater water loss through the epidermis to the skin surface, from where it evaporates.
- The de-fatted skin may become excessively dry.
- The surface horny cells may be loosened, disturbing barrier function and allowing more water loss. The skin becomes more permeable to chemicals such as hair dye and perming solution.
- Dry skin is more prone to infection with Staphylococcus aureus, resulting in impetigo.
- Irritant contact dermatitis (red, dry, chafed skin) may develop. This may be provoked by the dry skin itself, or by a particular surfactant in the shampoo. Note that sodium lauryl sulphate may be more irritating than sodium laureth sulphate.
- Stinging, especially if dermatitis is already present.
- Contact urticaria (immediate redness, itching and swelling) may arise due to a fragrance or preservative.
- Allergic contact dermatitis (a delayed but persistent reaction) may develop to a component of the shampoo. Because they are rinsed off, true contact allergy to shampoo is rare. However it may result from:
- Protein contact dermatitis, a rare mixture of contact urticaria and allergic dermatitis, due to a protein component such as peanut or oatmeal.
The manufacturers of hypoallergenic shampoos have tried to avoid using substances that are likely to cause contact allergy. Their products are often "fragrance-free" (low levels of masking fragrances are permitted), "mild" and "non-irritating". If you have oily skin (seborrhoea), choose shampoo designed for your skin type.
Labelling in the USA
For the US, the FDA states: "If a cosmetic claim is made on the label of a "true" soap or cleanser, such as moisturizing or deodorizing, the product must meet all FDA requirements for a cosmetic, and the label must list all ingredients. If a drug claim is made on a cleanser or soap, such as antibacterial, antiperspirant, or anti-acne, the product is a drug, and the label must list all active ingredients, as is required for all drug products."
There are no specific labelling requirements in New Zealand.