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Soaps and cleansers

Author: Dr Amanda Oakley MBChB FRACP, Dept of Dermatology Waikato Hospital, Hamilton, New Zealand, 1999.


Why wash?

Everyone likes to feel clean; it's refreshing, invigorating, relaxing and enjoyable. Washing your skin removes excessive oil and unpleasant odours as well as make-up, sunscreens and dirt.

How to wash

Gently wash affected areas on waking, post-exercise and at bedtime. Wet skin. Apply soap or cleanser to hands, add warm water and work into lather. Massage gently. Rinse thoroughly. Gently pat dry.

Do I have normal, dry, oily or sensitive skin?

These terms are most frequently applied to facial skin, but may apply to other sites as well. To determine your skin type, wash your face and pat dry. Wait for an hour, then press a tissue to your forehead, cheeks, chin and nose. If your face is not shiny and there's no oily residue on the tissue, you have normal skin. If your face looks/feels tight or is flaky and there is no oily residue on the tissue, you have dry skin. If your face is shiny and the tissue reveals an oily residue, you have oily skin. Many people have combination skin: the T-zone (forehead, nose, chin) is oily but the cheeks are normal or dry.

Normal skin has a correct balance of moisture and oils. It is slightly acidic at a pH of 4.5–5.75 (6.5 under the arms). A variety of harmless (commensal) bacteria and yeasts live in low numbers on the skin surface, and may help protect your skin from infection (invasion by more harmful bacteria such as staphylococcus or streptococcus).

Sensitive skin is skin that stings easily, especially during or just after cleansing. Sensitive skin is more likely to be dry and is hyper-reactive, that is, prone to develop dermatitis (itchy bumpy skin). Sensitive skin may be inclined to be red, flush easily or have broken capillaries (telangiectasia).

There is often an underlying skin problem such as:

What do cleansers contain?

There is a wide range of products designed for washing, available as bars, liquids, gels, creams, shampoos, scrubs, masks, cloths and wipes. When designing their products, manufacturers consider mildness, biodegradability, low toxicity, cleansing ability, emulsification, moisturisation, convenience, skin appearance and feel, smell (fragrance) and lubrication. The cost varies greatly — although the ingredients of an expensive product may be similar to an inexpensive one.


Pure water alone is not quite enough: removing dirt, which is fat-soluble (lipophilic) and sticks to the skin, requires a surfactant  (surface-active agent). Surfactants may be a soap, a synthetic detergent or a combination. They help determine the product's lathering characteristics, feel on the skin, and how easily it rinses off.

Surfactants consist of a fat-soluble (lipophilic) part and a water-soluble (hydrophilic) part.

  • The lipophilic part sticks to oil and dirt, loosening particles from the skin surface.
  • The hydrophilic part allows it to be washed away.

Surfactants often have an electrical charge.

  • Anionic (negatively charged) surfactants foam (lather) and include sodium lauryl sulphate, sodium laureth sulphate and sodium sulphosuccinate. Anionic surfactants rinse off easily.
  • Cationic (positively charged) surfactants include trimethyl dodecyl ammonium chloride.
  • Amphoteric surfactants such as cocamide propyl betaine are both negatively and positively charged. They are pleasant to use and reduce the irritant action of anionic surfactants. 
  • Non-ionic surfactants include polyethylene glycols (PEGs) and acyl-polyglycoside (APG).

Other ingredients

  • Water to remove water-soluble (hydrophilic) components of dirt.
  • Emulsifiers such as diethanolamine (DEA) to prevent separation into layers of different chemicals.
  • Moisturisers to replace skin oils and retain moisture in the skin.
  • Fragrances to provide a pleasant smell.
  • Preservatives to prolong shelf-life and prevent mould.
  • Colours, humectants, thickeners and solvents such as glycerine to improve texture and appearance.
  • Biocides (antiseptics) such as triclosan and para-chloro-meta-xylenol (PCMX), to reduce cutaneous bacteria. They can reduce body odour and help certain skin disorders such as atopic dermatitis and acne. These products, depending upon their formulation and application, may also kill or inhibit the growth of bacteria that cause intestinal illnesses and other community infections. But there is concern that common household use of antibacterial soap may increase resistant organisms and actually make such infections more likely and more serious. The FDA has ruled that consumer antiseptic wash products containing certain active ingredients such as triclosan can no longer be marketed in the USA.
  • Scrubs are abrasive substances to smooth out rough skin or remove stubborn dirt. They are found in industrial hand cleansers.
  • Antioxidants, vitamins and alpha-hydroxy acids (fruit acids) to smooth skin and reduce photoaging changes.
  • Botanicals to soothe, heal, moisturise, for their astringent properties or to act as natural antiseptics.
  • Exfoliating (peeling), keratolytic (skin-dissolving) or comedolytic (whitehead-removing) additives such as salicylic acid or benzoyl peroxide to reduce acne.

What are the complications of skin cleansing?

Soaps and cleansers can irritate and result in skin problems. These are rare with modern synthetic detergent products made by reputable manufacturers if they have been designed for sensitive skin and are used appropriately. Over-washing may have the following effects:

  • The pH of the skin may change. Water alone has a neutral pH of 7. Soaps are alkalis pH –12, which damage the skin barrier function.
  • The number and type of bacteria may change. Alkalis may increase the number of Cutiibacterium acnes (the acne bacteria).
  • The surface oil film (sebum) is removed, allowing greater water loss through the epidermis to the skin surface, from where it evaporates. This may lead to dermatitis.
  • 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.
  • 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 cleanser. Sodium lauryl sulphate is more irritating than sodium laureth sulphate. Cleansers designed to treat acne should be used with caution if leave-on acne products are used as well: too much treatment will result in excessive dryness and irritation.
  • Stinging is particularly likely with alcohols, gels, alpha-hydroxy acids and other additives
  • Contact urticaria (immediate redness, itching and swelling) may arise due to fragrance, preservative or benzoyl peroxide.
  • Some formulas may cause comedonal acne.
  • Scrubbing may break open comedones resulting in inflammatory acne.
  • Applying a thick moisturiser to compensate for dryness could also aggravate acne.
  • Allergic contact dermatitis may rarely develop to a component of the cleanser.  
  • Protein contact dermatitis, a rare mixture of contact urticaria and allergic dermatitis, due to a protein component such as peanut or oatmeal.


Soap has been made since ancient times but has been particularly popular for cleansing the body since the mid-eighteenth century when modern manufacturing processes were discovered.

Soap is an anionic surfactant. Soap is made from fat and oil mixed with an alkali, forming glycerine and the sodium salt of the fatty acid. The fats required for soap making come from a combination of tallow, grease, fish oil, or vegetable oil. In ancient times, the alkali came from ash but today the alkali for solid bar soap is sodium hydroxide. Liquid soaps are made with potassium hydroxide.

The hardness, lathering ability, and transparency of soap vary according to the combination of ingredients.

Disadvantages of soap

  • Soap is alkaline, which irritates sensitive skin, which is normally acidic. Alkaline skin degrades quickly as protease enzymes are activated that destroy the skin proteins.
  • Soap forms scum when used with hard water (water that contains a high amount of calcium in solution). The scum stops the surfactant properties, so one tends to use more soap.
  • Soap leaves deposits of carbonate salts on the skin. This irritates the skin.
  • Soap deteriorates on storage.


Synthetically produced detergents (syndets) were developed in the 1950s and are widely available. They are made from a variety of petrochemicals (derived from petroleum) and/or oleochemicals (derived from fats and oils). These hydrocarbon chain sources are used to make the lipophilic end of the surfactant molecule. Chemicals, such as sulphur trioxide, sulphuric acid and ethylene oxide, are used to produce the hydrophilic end of the surfactant molecule.

Compared with soap, syndets:

  • Can be set to the normal skin pH of 5.5
  • Reduce follicular Cutibacterium acnes
  • Do not produce scum, so they rinse off 
  • Cause less dryness 
  • Are less likely to irritate sensitive skin 
  • Are more expensive.

Hypoallergenic products

The manufacturers of hypoallergenic skin cleansers 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 acne, choose products that are labelled as "oil-free" and "non-comedogenic".

Hypoallergenic products may still be irritating to those with very sensitive skin, and they may still rarely cause contact allergy.

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.



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