Shampoo

What is shampoo?

A shampoo is a cleanser designed to clean the hair and scalp by removing sebum, sweat, corneocytes (dead keratinocytes), fungi, dirt, and hair care products.

What are the types of shampoo?

• Normal hair shampoo — intended for scalps with typical sebum production and virgin (unprocessed) hair
• Everyday shampoo — mild detergent formulation designed for daily use without overcleansing or irritation
• Dry hair shampoo — maintains scalp moisture by using a mild, conditioning surfactant that cleanses with minimal sebum stripping
• Damaged hair shampoo — mild cleanser with protein derivatives that deposit onto the damaged hair shaft  
• Oily hair shampoo — targets scalp seborrhoea by cleansing with minimal conditioning
• Deep cleaning (clarifying) shampoo — similar to oily hair shampoo, which thoroughly cleanses without conditioning; recommend weekly rather than daily use to avoid overcleansing.
• Baby shampoo — incorporates mild amphoteric surfactants with minimal fragrance and a near skin-neutral pH (5.5-7.0); formulated to minimise irritation and allergenic potential; not designed for adult hair, but may be appropriate for damaged hair or dermatitis-prone scalps
• Conditioning (2-in-1) shampoo — combines cleansing and conditioning for convenience; can be used for daily washing.
• Hair dye shampoo — acidic shampoo used after dyeing to neutralise alkaline hair dyes; seals the cuticles to trap colour pigment inside and prevent hair damage.

Medicated shampoos are typically found over-the-counter and treat conditions such as seborrhoeic dermatitis, scalp psoriasis, and scalp atopic dermatitis. Ingredients may include:

• Tar derivatives — keratoplastic/cytostatic (reduces keratinocyte turnover), antipruritic
• Salicylic acid — keratolytic
• Zinc pyrithione — antifungal, antibacterial
• Ketoconazole — antifungal
• Selenium sulfide — antifungal, cytostatic
• Corticosteroids — anti-inflammatory. 

Shampoo formulation and ingredients

Shampoos can be formulated as aqueous solutions (most common), emulsions, liquids, lotions, gels, pastes, creams, and dry-powder sprays (‘dry shampoo’). 
They consist of detergents, conditioning agents, and additives.

Detergents


Detergents are surfactants used specifically to cleanse the scalp. Surfactants are amphiphilic molecules — that is, they possess a hydrophilic (water-soluble) head and hydrophobic (oil-soluble) tail, allowing sebum and dirt to be rinsed away with water.

Detergents are classified into four categories:

• Anionic detergents
  • Hydrophilic head is negatively charged
  • Most effective and widely used cleansing surfactant
  • Can be harsh and cause scalp dryness, static electricity, and rough hair
  • Examples: lauryl sulfates, laureth sulfates, sarcosinates, sulfosuccinates
• Cationic detergents
  • Hydrophilic head is positively charged 
  • Adhere to and neutralise the negatively charged hair shaft, reducing static and frizz
  • Flatten cuticle scales, reducing inter-fibre friction and improving smoothness and combability
  • Possess mild antimicrobial properties 
  • Poor cleansers mainly used for conditioning
  • Examples: Quaternary ammonium compounds (such as cetrimonium, behentrimonium, and benzalkonium chloride), guar hydroxypropyltrimonium chloride, polyquaternium-10
• Non-ionic detergents
  • Hydrophilic head carries no electrical charge
  • Second most commonly used detergent class
  • Mild and typically used as a secondary cleanser alongside another surfactant 
  • Examples: alkanolamides (such as cocamide MEA/DEA), alkyl polyglucosides (such as coco-, decyl-, or lauryl glucoside), polysorbates, alcohol ethoxylates 
• Amphoteric detergents
  • Switches between cationic and anionic depending on pH
  • Non-irritating to the eyes and foam moderately well 
  • Examples: betaines, sultaines, imidazolinium derivatives.

Shampoos can combine different types of surfactant to achieve the desired detergent effect.

Conditioning agents

Conditioners counteract the effects of detergents and are found in shampoos designed for dry, damaged, or chemically treated hair. They:

• Moisturise the hair shaft (sebum-mimicking)
• Minimise hair static
• Temporarily bind split ends
• Smooth, soften, and add shine by flattening the hair cuticle.



Common conditioning substances in shampoos include:

• Cationic surfactants (see above)
• Protein derivatives eg, hydrolysed keratin, wheat, rice, silk, or animal proteins
  • Temporarily patch hair shaft damage and improve tensile strength
  • Deposits add thickness and create a volumising effect
• Silicones eg, dimethicone, cyclomethicone, amodimethicone
  • Form a thin film over the hair shaft after rinsing, reducing friction and hair breakage.

Additives

Additives include:

• Foaming agents eg, cocamide DEA, cocamidopropyl betaine
  • Foaming agents are surfactants that introduce and stabilise air bubbles, creating richer and longer-lasting lather (foam)
  • Lather does not directly cleanse but helps spread the detergent over the hair and scalp
• Fragrances
• Opacifiers and thickeners to improve optical and textural quality
• Preservatives to inhibit microbial growth
• Sequestering agents (eg, EDTA, polyphosphates, citric acid) chelate minerals to prevent soap scum formation when mixed with hard water
• Speciality additives to address specific needs or enhance marketability. 

Steps of proper shampooing

• Wet the scalp and hair using warm or cool water (hot water can be drying).
• Dispense a coin-sized amount of shampoo onto the palm and rub hands together to evenly distribute.
• Massage the shampoo gently into the scalp for about 30 seconds to form lather.
• Rinse thoroughly.
• A second round of shampooing may be required for oily scalps. 

Shampoo should be easy to rinse off, but conditioner, styling products, and chemical processes may leave a residue.

Medicated shampoos should be left on the scalp for at least 5 minutes before rinsing off.

Shampoo-associated skin problems

• Allergic contact dermatitis (ACD) to shampoo is relatively uncommon because allergens are quickly rinsed off, reducing the risk of an allergic reaction.
  • Allergens in shampoo include but are not limited to: formalin, paraben, hexachlorophene, botanicals (eg, chamomile, lavender oil), fragrances, preservatives (eg, Kathon CG, quaternium-15)
  • Eczema distribution in a distinctive ‘rinse-off’ pattern (eg, around the hairline, behind the ears) is suggestive of ACD to shampoo or other hair care products.
• Overwashing and/or use of harsh surfactants can excessively strip away the surface oil film (sebum), resulting in dry and irritation-prone skin
  • This can exacerbate symptoms of scalp psoriasis, atopic dermatitis, acne, and seborrheic dermatitis.
  • Irritant contact dermatitis may be provoked by the dry skin itself, or by a particular surfactant in the shampoo; sodium lauryl sulphate may be more irritating than sodium laureth sulphate.
• Shampoo residue left behind by inadequate rinsing can accumulate and occlude hair follicles, contributing to ‘pomade acne’ (acne along the hairline). 
• Contact urticaria (immediate redness, itching, and swelling) may arise due to a fragrance, preservative, or protein hydrolysate.