Most people choose shampoo by looking at the lengths: dry, colored, fine, frizzy hair. In reality, shampoo works mainly on the scalp, which is skin in every respect, with its sebaceous glands, sweat, and pH. The lengths are cared for by conditioner.
This article explains how shampoo is made, what distinguishes the different types, and how to choose one based on the scalp.
Article written by Elisa Avalle, founder of LeLang Skin Care and a dermocosmetics specialist. Cover image generated with the support of artificial intelligence.
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What shampoo is really for
Much of the dirt on the scalp comes from the skin itself: sebum, sweat, shed cells, and oxidized sebum residue. Dust, smog, and residue from styling products add to this.
The purpose of shampoo is to remove excess oil without over-degreasing. If it cleanses too aggressively, it also removes the thin lipid film that protects the hair: the lengths become dull and rough, tangle, and build up static electricity. The scalp, in turn, may react with dryness, itching, or a rebound increase in sebum production.
The right shampoo is the one that cleans enough without over-cleansing. That's why there is no single best shampoo: there is one suited to each specific scalp.
How shampoo is made
The foundation of every shampoo is surfactants, the substances that create foam and remove grease. Generally, there is one primary surfactant, which does most of the work, and one or more secondary surfactants, which make the formula gentler and the foam creamier.
- Primary surfactants: the most common are sulfates, such as sodium laureth sulfate. They cleanse well and are inexpensive, but they have the strongest degreasing effect.
- Secondary surfactants: betaines and amphoacetates, which are gentler and reduce the formula's irritating potential.
- Conditioning agents: silicones, cationic polymers such as polyquaterniums, hydrolyzed proteins, panthenol. They reduce the degreasing effect and make hair easier to comb.
- pH adjusters: usually citric or lactic acid, which bring the shampoo to a pH between 5.5 and 6.5, close to that of the scalp, which is slightly acidic.
- Preservatives: shampoo is made mostly of water, and without preservatives it would become a breeding ground for bacteria and mold.
The main types of shampoo
Gentle or frequent-use shampoo
It uses milder surfactants instead of sulfates: glucosides, betaines, isethionates, sarcosinates. It is gentler on the lipid barrier and is the basic choice for those who wash their hair often, even every day.
2-in-1 shampoo
It adds a conditioning component to the cleanser, usually a cationic surfactant and silicones. It is convenient, but it is a compromise: not very suitable if the scalp is oily, because it leaves an extra film, and often insufficient if the hair is very dry.
Shampoos specifically for the scalp
They contain active ingredients targeted at a specific condition: excess sebum, dandruff, or sensitivity. Here, shampoo becomes part of a treatment and should be chosen based on what is happening on the skin. There is more information about dandruff in how to identify dry and oily dandruff.
Repairing shampoo and shampoo for color-treated hair
The repairing shampoo contains proteins and amino acids that deposit on the hair fiber damaged by bleaching, dyeing, and heat. Shampoo for color-treated hair has an even gentler cleansing base, to remove less pigment, and a slightly more acidic pH, which helps keep the cuticle scales closed.
Dry shampoo
It doesn’t cleanse: it absorbs. It is a powder that traps sebum and makes the roots look more presentable between washes. Useful when traveling or when you can’t wet your hair, but it does not replace washing.
Sulfate-free and silicone-free: what changes
The trend in recent years has been to remove the most oil-stripping sulfates and replace them with milder surfactants. For a sensitive or dry scalp, this is a real advantage; for a very oily scalp, on the other hand, a shampoo that is too gentle may not be enough.
Silicones have a different role: they don’t cleanse, they coat. They make hair smooth and shiny, but water-insoluble silicones can build up with washing and weigh hair down, especially fine hair. They are not harmful to the scalp: it’s a matter of performance, not safety.
“Sulfate-free” and “silicone-free” do not automatically mean “better.” They mean different, and should be chosen based on the scalp and hair type.
How to choose: start with the scalp
- Oily scalp, which gets dirty within a day or two: gentle or sebum-regulating shampoo, which can also be used every day. It’s best to avoid 2-in-1 products and very rich products at the roots.
- Dry or tight scalp: gentle, sulfate-free shampoo and washing with water that isn’t too hot.
- Sensitive or itchy scalp: a simple, lightly fragranced formula with mild surfactants. If itching is frequent, it is best to understand its cause before changing products.
- Normal scalp and dry or treated lengths: use a gentle shampoo at the roots and conditioner or a mask on the lengths.
How to wash your hair properly
- Thoroughly wet your hair with lukewarm, not hot, water.
- Dilute the shampoo in your hands and distribute it over the scalp, not the ends.
- Massage with your fingertips, never your nails, for one minute.
- Rinse very thoroughly: the foam that runs down is enough to cleanse the lengths.
- A second wash is only needed if your hair is very dirty or if you use a lot of styling products.
Frequently asked questions
Is washing your hair every day harmful?
No, if the shampoo is gentle. The right frequency is whatever the scalp needs: people who produce a lot of sebum can wash their hair every day without problems, while those with dry skin can space out washes.
Does shampoo cause hair loss?
No. Washing dislodges hairs that were already at the end of their growth cycle and would have fallen out anyway. We discuss this in the article about hair loss in autumn.
Do you need to change shampoo occasionally because hair gets used to it?
No, hair does not get used to it. It makes sense to switch when the scalp changes, for example with the seasons, or when product residue builds up.
Is baby shampoo gentler for adults too?
It is formulated not to irritate the eyes, with very mild surfactants and a near-neutral pH. It may work well for a sensitive scalp, but it is often not enough to cleanse an oily scalp.
Sources for this article
Gavazzoni Dias M.F.R. “Hair cosmetics: an overview”, International Journal of Trichology, 2015. Gavazzoni Dias M.F.R. et al. “The shampoo pH can affect the hair: myth or reality?”, International Journal of Trichology, 2014. Regulation (EC) No. 1223/2009 on cosmetic products.
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