Is sulfate-free shampoo better? When it helps and when it does not

What sulfates are

Sulfates are cleansing agents. The two most common in shampoo are sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). They belong to a group of cleansers called anionic surfactants, which carry a negative charge and pull oil and dirt off the hair and scalp so water can rinse it away.

A review of shampoos in the Indian Journal of Dermatology describes lauryl sulfates as popular main cleansers that work in both hard and soft water and produce a rich foam. The same review describes laureth sulfates as good cleansers with good foam that suit normal to dry hair. Laureth sulfate is the milder of the pair, and a shampoo that leaves out SLS while keeping SLES is gentler, though still a sulfate shampoo.

Sulfate-free shampoos still contain cleansers. They use milder ones, often with names ending in betaine, glucoside, isethionate or sarcosinate on the ingredient list. These lather less and remove less oil per wash.

What sulfates do to hair

The strength of sulfates is also their cost. The Indian Journal of Dermatology review warns that hair that has been over-cleaned is harsh, rough and dull, with frizz, and tangles more easily. It recommends lauryl sulfates for oily hair with the note that such hair needs careful conditioning.

The charge matters too. A review of hair cosmetics in the International Journal of Trichology explains that strong anionic cleansers can increase the negative electrical charge on the hair surface and increase frizz and friction. Hair strands with the same charge push away from each other, which is part of what frizz is. Conditioners carry a positive charge and reduce that effect, which is why conditioning after a sulfate shampoo matters so much.

Dr. Melissa Piliang, a dermatologist at Cleveland Clinic, puts it simply: sulfates clean by attracting oil and dirt, but they can make hair more prone to breakage and irritate the scalp.

What sulfates do to the scalp

Sodium lauryl sulfate irritates skin, and this is well documented, because dermatologists use it on purpose. In patch testing, SLS is applied to the skin as a standard irritant to measure how easily a person's skin reacts. A study in the European Journal of Dermatology used SLS at 0.125 to 1 percent and found that the skin reaction grew stronger as the concentration went up.

A patch test holds SLS against the skin for 48 hours, and shampoo sits on the scalp for a minute or two before it is rinsed away. The patch test shows what SLS can do to skin under strong conditions. For shampoo, the practical point is narrower: a scalp that already stings, itches or reddens easily has a real reason to try a sulfate-free shampoo first.

If your scalp itches or flakes, the cause may be something else. Dandruff, for example, needs a shampoo with a specific active ingredient. The American Academy of Dermatology lists zinc pyrithione, salicylic acid, sulfur, selenium sulfide, ketoconazole and coal tar as the ingredients to look for. Some dandruff shampoos are sulfate free, and the active ingredient is what treats the flaking. If flaking continues after using one of those, see a dermatologist.

When sulfate-free helps

Dry hair. Hair that feels rough and takes in conditioner quickly already has too little oil along its length. A milder cleanser leaves more of that oil in place. Our post on why hair stays dry even with conditioner goes through the other causes of dryness.

Curly and coily hair. Curls are drier along the length because scalp oil travels down a curled hair less easily. The International Journal of Trichology review notes that curly and wavy hair is more likely to have an oily scalp but a drier hair fibre, because the oil is hard to spread along a curl. The American Academy of Dermatology recommends a moisturising shampoo made for curly hair, and many of those are sulfate free.

Coloured and bleached hair. Permanent colour works by opening the outer scales of the hair so the dye can reach the inside, and bleach does the same. Hair treated this way loses moisture faster and takes more damage from each strong wash. A gentler shampoo is a sensible choice. Its effect on fading is limited, for a reason explained in the next section.

Sensitive scalps. For the reasons above, a scalp that reacts easily is a good case for a sulfate-free trial of a few weeks.

Colour: what sulfate-free can and cannot do

Many people switch to sulfate-free shampoo to keep colour from fading. The evidence here is limited. A study in the Journal of Cosmetic Science found that fading of permanent hair colour during washing happens mainly because the dye dissolves into water. The type of cleanser was one factor the researchers tested, alongside pH and hair type.

In practice, that means water is doing much of the fading, whatever the shampoo. Washing less often, using cooler water, and conditioning every time all help colour last. A sulfate-free shampoo is a sensible part of that routine, and one part among several.

Sulfate free and colour safe are separate claims. Sulfate free lists what is left out. Colour safe is a claim the maker tests or defines for itself. Most colour-safe shampoos are sulfate free, and a sulfate-free shampoo has not always been tested on coloured hair.

When sulfate-free does not help

Oily scalps. A scalp that makes a lot of oil needs a shampoo that removes it, and sulfates do that well. With a gentler shampoo, oily roots can look greasy by the next day. If you want to stay sulfate free, washing twice in the same shower often solves it. Our guide on oily roots and dry shampoo covers the routine for an oily scalp.

Heavy product users. Styling creams, gels, silicone serums, oils and dry shampoo build up. The Indian Journal of Dermatology review explains that the polymers in styling products build up on the hair with continued use and need a strong detergent such as a lauryl sulfate to remove them. A sulfate-free shampoo on its own may not keep up. A clarifying wash every few weeks, with a sulfate shampoo, clears the layer.

Fine hair with an oily scalp. Fine hair shows oil and weight sooner than thick hair. A rich sulfate-free shampoo can leave it flat. A light formula, or a regular shampoo, often works better.

Hair loss. Changing shampoo will not treat hair loss. Dr. Piliang at Cleveland Clinic says you can buy shampoos that are better or worse for your hair, but none treat hair loss. She also notes that people often mistake breakage for shedding, and that harsh shampoos can add to breakage. If your hair is thinning or shedding heavily, see a doctor or dermatologist.

How to read the label

The words on the front of a bottle are a claim by the maker. The ingredient list on the back is more useful, because it follows a rule. In the United States, cosmetic ingredients must be listed in descending order of predominance, which means the ingredient present in the largest amount comes first. Ingredients at 1 percent or less can follow in any order.

In a shampoo, water is usually first and the main cleanser is usually second or third. So look at the first few ingredients:

• Sodium lauryl sulfate or ammonium lauryl sulfate near the top: a strong cleanser. Good for oily scalps and for removing buildup, and the most likely to leave dry hair rough.
• Sodium laureth sulfate or ammonium laureth sulfate near the top: a sulfate, and a milder one. Many everyday shampoos for normal hair use it.
• No sulfate in the list: a sulfate-free shampoo. The cleansers will be further down the scale of strength.

The rest of the list matters too. Two sulfate-free shampoos can feel different on the same hair, because conditioning ingredients, oils and fragrance change the result. If one sulfate-free shampoo leaves your hair flat or your scalp itchy, a different one may not.

How to decide for your own hair

Start with the scalp. The American Academy of Dermatology advises applying shampoo to your scalp instead of the entire length of your hair, so the shampoo's main job is cleaning the scalp. If your scalp is oily, a shampoo with sulfates may suit it. If your scalp is dry or sensitive, sulfate free is the better start.

Then look at the lengths. Conditioner looks after the lengths far more than the shampoo does, so dry, curly or coloured lengths need conditioner every wash whatever shampoo you use.

Give any change a few weeks of normal washing. Hair and scalp take a few washes to settle, and the first week after a switch often feels different without being better or worse. If your hair feels coated or your roots look greasy by then, add a clarifying wash or go back to a shampoo with sulfates. If it feels softer and your scalp is calmer, stay with it.

Our post on whether hair gets used to shampoo explains why a shampoo can seem to stop working, and what is usually happening instead.