Dr Mir Malkani — Updated on April 7, 2025
Keratin makes up 65% to 95% of your hair fibre [1]. It’s an essential protein for keeping your hair strong and healthy — but your body can’t absorb keratin from food or other sources, so many people turn to keratin hair treatments that are designed to strengthen your hair [2].
But keratin treatments may not be as beneficial as they sound. So it’s important to do your research before applying any keratin treatments.
In this article, we’ll explore the pros and cons of keratin for hair, including what keratin is, how keratin treatments work, and how to care for keratin-treated hair.
- What is keratin and what does it do for your hair?
- Are keratin treatments good for your hair?
- What are keratin hair treatments?
- Are keratin treatments bad for your hair?
- Keratin for different hair types
- How long do keratin hair treatments last?
- Types of keratin hair treatment
- How to care for keratin-treated hair
- Get haircare and hair loss advice from our trichology team
- Keratin for hair FAQs
What is keratin and what does it do for your hair?
Keratin is the key structural building block of your hair, skin, and nails. Each part of the hair — including the medulla, cortex, and cuticle — consists mainly of keratin proteins [3]:
Keratin gives your hair its shape. For example, people with Afro hair styles tend to have wavy, curly, or coiled hair. Some studies have shown that keratin is responsible for different hair textures [4].
The cortex is surrounded by the hair cuticle, which is made up of dead skin cells that protect the hair cortex. The hair cuticle is easily damaged by exposure to harsh environments and styling treatments. This causes the cuticle to lift, leading to split ends, breakage, and frizz.
Keratin is essential for keeping your hair in tip-top condition. That’s why it’s important to eat protein-rich foods that contain amino acids that promote keratin production in your hair. Good sources of protein and amino acids include:
- Lentils and beans
- Greek yoghurt
- Tofu
- Eggs
- Meat and poultry
- Salmon
- Oily fish
Are keratin treatments good for your hair?
Some studies have shown that topical keratin treatments can make your hair feel smoother and glossier. They’re sometimes used to relax hair in those with curly hair types, such as people with 3a hair.
However, some evidence shows that while keratin treatments can give you aesthetically pleasing results, the formulas aren’t actually always safe to use [5-6]. But before we get into the dangers of applying keratin treatments to your hair, let’s take a look at some of the benefits:
- Improve hair texture — Keratin treatments can help flatten the hair cuticle, making your hair feel smoother. This may be beneficial if you have damaged hair caused by heat or excessive styling.
- Strengthen your hair strands — Keratin treatments can make your hair stronger and more resistant to damage. One study found that keratin-based particles could improve the tensile strength of hair by up to 40% [7].
- Frizz reduction — Smoothing out your hair cuticles can reduce flyaways and frizz, making your hair shinier and more manageable.
- Reduce hair drying time — Keratin treatments may make your hair less porous, meaning it absorbs more water but doesn’t retain it in the cuticle. That means you won’t need to expose your hair to damaging hairdryers for as long.
- Improve the appearance of split ends — Split ends are a leading cause of hair thinning in women. While keratin treatments can’t repair split ends, they can temporarily improve their appearance, making your hair look thicker and fuller through the lengths.
What are keratin hair treatments?
Keratin treatments are hair products designed to smooth out your hair, making it feel softer and appear shinier. When applied to your hair, these treatments add keratin proteins to your strands, which can repair bonds or fill gaps that have damaged the hair shafts over time.
However, keratin must be activated in order to repair this damage and improve hair texture. Currently, the only way to activate keratin is to apply heat and other chemicals — such as formaldehyde — to interact with the keratin in your hair and change its structure [5].
This is known as cross-linking; chemical bonds are formed between the existing and applied keratin molecules, leading to improved hair texture and reduced frizz.
Here are the results of one study that applied keratin K31 topically to the hair shafts. Researchers noted a reduction in frizz and straighter hair after just one treatment:
However, the chemicals used in keratin treatments could be dangerous. So what do these treatments contain?
Are keratin treatments bad for your hair?
While there are undoubted aesthetic benefits to using keratin treatments, you should also be aware of the underlying dangers.
Traditionally, keratin treatments contain formaldehyde — a flammable, colourless chemical that can cause adverse side effects like nausea, nosebleeds, and skin irritation, especially if you’re exposed to formaldehyde fumes repeatedly over time. Formaldehyde exposure has also been linked with cancer, which has led to restrictions on its use in the UK and other countries [8].
Nonetheless, a study from 2014 found that six out of seven commercial Brazilian keratin treatments contained more than five times the recommended exposure level of formaldehyde [9].
Know your keratin treatment ingredients
Not all treatments contain formaldehyde these days, due to its known risks. But they do contain other ingredients that release dangerous compounds when the treatment is applied [10-11]. Some of these compounds are known carcinogens.
This loophole means you could still be exposing your hair and scalp to dangerous compounds whenever you have keratin for hair treatment.
Ingredients that can release toxic compounds when exposed to heat or water include:
- Glyoxylic acid
- Glyoxyloyl carbocysteine
- Cyclopentasiloxane
- Dimethicone
- Phenyl trimethicone
These so-called formaldehyde-free formulas may release less formaldehyde than other keratin treatments, but they can still expose you to dangerous levels of toxic chemicals.
If you’re keen to try a keratin treatment, it’s important to know exactly what’s going on your hair before you do it. Speak to your stylist about the ingredients in the treatment they use.
Keratin for different hair types
If you decide to go ahead with a keratin treatment, it’s important to know it could affect your hair type. Here are the results you might expect from keratin for different hair types.
1. Keratin for thin hair
Thin hair often benefits the least from keratin treatments, especially if you already have relatively straight hair. That’s because thin hair may already be affected by breakage or damage, which can be exacerbated by harsh keratin treatments.
That said, some people with thin hair like the effect of keratin treatments. Thin hair can still be curly or frizz-prone, both of which can be improved with keratin formulas.
2. Keratin for curly hair
Keratin treatments are becoming increasingly popular for those with Afro and curly hair types as an alternative to hair relaxers. Relaxers can be painful and damaging if used repeatedly.
Keratin treatments usually make curly hair easier to manage. It becomes less prone to knotting and tangling, and reduces frizz.
However, the effects of keratin treatments are semi-permanent. So if you want to flip between your natural curls and straighter hair, keratin may not be the best option.
3. Keratin for straight hair
Keratin treatments can smooth out naturally straight hair that’s prone to frizz.
However, it won’t add volume, so if you’re looking for more hair texture, keratin probably isn’t the best choice.
4. Keratin for coloured hair
You can use keratin treatments on dyed hair but should do so cautiously. That’s because hair dyes and bleaches can interact with your hair in unexpected ways after chemical treatments, potentially leading to significant damage and ruining your hair colour:
Keratin treatments can also change the tone of your hair, so make sure you’re aware of this possibility before applying keratin treatments to your dyed or bleached hair.
It’s also important to take note of which formulas have been used on your hair in the past, so you can inform future stylists. This will help them choose products that are safe for your hair.
How long do keratin hair treatments last?
Keratin hair treatments are semi-permanent, which means they typically last between three and six months. To retain your smoother, straighter style after this, you’ll need regular top-up treatments.
Types of keratin hair treatment
There are multiple types of keratin for hair:
- Salon keratin treatments — Also known as Brazilian Blowouts, in-salon keratin treatments are one of the most popular ways to apply keratin for hair. They use keratin, chemicals, heat, and compression to reset the hair structure. However, depending on which formula is used, they can expose you (and your stylist) to harmful chemicals.
- Keratin oil treatments — Keratin is mixed with argan oil or other healthy hair oils to smooth your hair and reduce frizz at home. The oils also moisturise your hair, adding to its shine.
- Keratin hair masks — A hair mask is an intensive hair treatment designed to moisturise and treat damaged hair. They’re usually applied to wet hair and left in for at least five minutes to allow your hair to absorb the keratin and other ingredients.
It’s not just in-salon treatments that can contain harmful ingredients. Certain home formulas also use the ingredients listed above, which can release toxic chemicals when heat is applied at home. So check the ingredients list before you buy.
How to care for keratin-treated hair
If you have your keratin treatment in a salon, ask your stylist for aftercare advice. They may recommend that you:
- Combine your keratin treatment with a trim to remove split ends.
- Avoid washing your hair for at least three or four days after treatment.
- Protect your hair with thermal protection spray if you curl or straighten it.
- Don’t go swimming in chlorinated water, as this can strip the hair of keratin. If you want to swim, wear a swimming cap.
- Avoid other chemical treatments (including bleaches and hair dyes) for at least a month after your keratin treatment.
Get haircare and hair loss advice from our trichology team
Keratin hair treatments are popular, as they can give your hair a renewed glossy appearance. But under the surface, these treatments can be harmful to your hair and your health.
In some cases, keratin treatments can even lead to hair loss or extreme hair damage. If you’ve experienced hair loss and think your treatment may have caused it, book a consultation with a Wimpole Clinic trichologist.
We specialise in helping uncover the causes of women’s hair loss, which are often varied and complex. Our team can then find the best female hair loss treatment to help your hair recover quickly.
Keratin for hair FAQs
Find out more about keratin for hair in these frequently asked questions.
Does keratin increase hair growth?
Keratin treatments won’t boost your hair growth, though they can make your hair appear longer as it becomes straighter and smoother.
That said, it’s really important to get plenty of protein in your diet so your hair can generate its own keratin, which helps promote healthy hair growth.
Does keratin cause hair thinning?
Keratin treatments can cause split ends and other types of hair damage, which often leads to breakage and the appearance of thinning ends.
However, they can also cause hair loss if you’re sensitive or allergic to the chemicals in your treatment. This is known as telogen effluvium, and it’s usually temporary. If this happens, it’s important to speak to a professional trichologist who can advise you on how to regain your hair.
Is it worth using keratin?
Keratin treatments can help improve the appearance of your hair temporarily, but it’s not a long-term fix. For best results, it’s important to make sure you’re eating a healthy hair diet, minimising the use of heat styling tools, and washing your hair regularly.
While keratin supplements are marketed as a way to strengthen your hair, there’s no evidence that they work. In fact, the body can’t absorb keratin directly, so you won’t benefit from keratin supplements. Instead, focus on eating protein-rich foods that will give your body the amino acids it needs to produce keratin.
- Hair Keratin | ScienceDirect
- “Let Food be Thy Medicine”: Value of Nutritional Treatment for Hair Loss
- The structure of people’s hair
- Human hair keratin network and curvature
- Effects of chemical straighteners on the hair shaft and scalp
- Brazilian keratin hair treatment: A review
- Keratin-based particles for protection and restoration of hair properties
- Formaldehyde and Cancer Risk | National Cancer Instiitute
- Elevated formaldehyde concentration in “Brazilian keratin type” hair-straightening products: a cross-sectional study
- The gas-phase photochemistry and thermal decomposition of glyoxylic acid
- Regarding the Evolution of Formaldehyde from Polydimethylsiloxanes
Talk to a specialist ☎ 020 7935 1861.
Dr Mir Malkani — Updated on April 7, 2025
Simply fill in your details and we’ll get in touch with you shortly.
Book a consultation
Simply fill in your details in the form below and we'll get in touch with you shortly.