Keratin Treatment / Brazilian Blowout (Hair Smoothing)
- Independent guide from The Hair & Beauty Directory
About Keratin Treatment / Brazilian Blowout (Hair Smoothing)
Keratin treatments and the Brazilian Blowout are semi-permanent hair-smoothing services that coat and bond a protein-based solution to the hair, which is then sealed with a flat iron. The aim is to reduce frizz, add shine and make hair easier to blow-dry and manage, rather than to permanently straighten it. Results are temporary and gradually wash out over roughly three to six months. The most important thing to understand is that some traditional smoothing products contain, or release, formaldehyde when heated, which is a recognised irritant and, at higher levels or with repeated exposure, a health concern for both clients and stylists. For this reason many reputable UK salons now use lower-risk, so-called formaldehyde-free systems based on ingredients such as glyoxylic acid, carbocysteine or amino acid complexes, though the smoothing effect and longevity can differ. The finish can be tailored, from a soft frizz-reduction that keeps some natural movement to a sleeker, straighter result, depending on the product, the number of passes with the iron and your hair type. A good salon will assess your hair and history first and be open about exactly which product they use and why.
On the day, and after
During the treatment
Expect the appointment to take around one and a half to three hours or more, depending on hair length and thickness. Your hair is usually washed with a clarifying shampoo to open the cuticle, then the smoothing solution is applied section by section and combed through. After a processing period the hair is blow-dried and sealed with a flat iron at high temperature, which is the stage that locks in the smoothing effect and, with formaldehyde-containing products, is when fumes are most likely to be released. You should notice good ventilation, and the stylist may wear a mask; if the room feels stuffy or your eyes, nose or throat start to sting, say so, as this can indicate formaldehyde in the air. The process is not usually painful, though the chemical smell and the heat near your scalp can feel intense. Your stylist can adjust the number of iron passes to give you a softer or sleeker finish to suit your hair and preference.
How it feels
During the treatment you can expect to notice a strong chemical smell and warmth near the scalp as the flat iron seals the product in. The process itself is not usually painful, and many people find it relaxing apart from the odour. Some clients feel mild tingling on the scalp. What you should not simply put up with is stinging or watering eyes, a burning sensation in the nose or throat, coughing or any tightness in the chest, as these can be signs of formaldehyde in the air and are a reason to pause, ventilate the room and step outside for fresh air. Afterwards the hair usually feels noticeably smoother, sleeker and easier to manage, and any faint product smell tends to fade after the first wash.
Results and maintenance
Hair smoothing gives a temporary result that gradually washes out rather than growing out in a hard line, so hair looks natural as it fades. Depending on the product and your hair, formaldehyde-free semi-permanent treatments often last around three to four months, while stronger systems such as a classic Brazilian Blowout may last four to six months. Longevity depends heavily on aftercare: using sulphate-free and salt-free products, washing less frequently, and protecting hair from chlorine, salt water and strong sun all help the effect last. The finish can be tailored at your appointment, from a soft reduction in frizz that keeps natural movement to a sleeker, straighter look. Bear in mind these treatments smooth and manage the hair rather than permanently altering the curl pattern, so your natural texture returns as the product wears off. Repeat treatments are possible, but avoid over-processing, and give your stylist a full history of any smoothing or straightening you have already had.
Before and after your appointment
Before your appointment
Book a consultation before your appointment so the stylist can assess your hair type, condition and any recent chemical services such as colour, bleach or other straightening treatments, as these affect suitability and the result. Ask which specific product will be used and request the Safety Data Sheet, as this shows whether the formula contains or releases formaldehyde and confirms it is being used correctly. Tell the salon if you are pregnant or breastfeeding, have asthma or a history of reacting to fumes, or have any scalp condition such as eczema, psoriasis or recent broken skin, as these may mean the treatment is not right for you. Come with clean, product-free hair unless told otherwise, and avoid colouring on the same day unless the salon advises the order. A strand test on a small section can help predict how your hair will respond. Make sure the salon is well ventilated, and raise any concerns openly beforehand rather than on the day.
Aftercare
Aftercare has a big influence on how long your results last. With many traditional keratin treatments you are advised to keep the hair dry, loose and unclipped for the first few days, typically up to seventy-two hours, avoiding washing, tying it back, tucking it behind your ears or using clips or hairbands that could leave a mark. Some newer formaldehyde-free systems allow washing sooner, so always follow the specific instructions your stylist gives you. After the settling period, use a sulphate-free and sodium-chloride-free shampoo and conditioner to protect the treatment, and wash less often, ideally two to three times a week. Chlorine and salt water can strip the smoothing effect, so wear a swim cap or apply a leave-in conditioner before swimming, and consider a hat in strong sun. Heat styling can be reduced but is not usually banned. If your scalp becomes irritated, itchy or sore afterwards, stop and seek advice from a GP or pharmacist.
There is generally no recovery time, and most people return to normal activities straight away. The main limitation is the settling period some products require, when the hair must stay dry and unmarked for up to seventy-two hours, so it helps to plan around exercise, swimming and washing. If you inhaled fumes during the treatment and feel mild eye, nose, throat or chest irritation, this typically eases in fresh air, but persistent coughing, wheezing, headaches or a skin reaction should be checked by a GP. Any lasting scalp soreness, redness or unusual hair breakage is worth reporting to the salon and a healthcare professional.
Safety and medical considerations
Safety essentials
The single most important safety issue with hair smoothing is formaldehyde, which can be released as a gas when the product is heated with a flat iron. It is a known irritant and is classed as a carcinogen at higher levels or with repeated exposure, which is why good practice centres on knowing what is in the product and controlling the fumes. Ask to see the Safety Data Sheet and choose a salon that is transparent about its formula and uses lower-risk or so-called formaldehyde-free options where possible. Note that some formaldehyde-free products can still release small amounts when heated, so ventilation matters regardless. The room should have good airflow or extraction, and the stylist should follow the manufacturer's temperature and timing instructions. Under UK workplace health and safety rules, salons should assess and manage these chemical risks for staff and clients. If you experience burning eyes, a stinging throat or breathing difficulty during treatment, ask them to stop and step into fresh air.
Medical considerations
Hair smoothing is a cosmetic service, not a medical one, but there are health situations where it is best avoided or delayed. Many salons and product makers advise against treatment during pregnancy or breastfeeding as a precaution, largely because of possible formaldehyde exposure, and it is sensible to discuss this with your midwife or GP. People with asthma or other respiratory conditions may be more sensitive to fumes and should take particular care over ventilation and product choice. Active scalp conditions such as eczema, psoriasis, dermatitis or broken or inflamed skin can be aggravated, so treatment is usually postponed until the skin has healed. If you have had a previous reaction to hair products or chemical fumes, tell the salon and consider seeking advice first. This information is general and not a substitute for personalised guidance; if you have any health concern, or symptoms that persist after treatment, speak to a GP or pharmacist.
Patch testing
A traditional allergy patch test is not the standard check for hair smoothing in the way it is for hair colour, but a proper pre-treatment consultation is important and, done well, protects both you and the salon. The stylist should review your hair condition, recent chemical services and any medical or scalp issues, and ideally carry out a strand test on a small section to see how your hair reacts and how straight it goes. This helps set realistic expectations and reduces the risk of damage or a poor result. From a UK liability point of view, a salon that skips consultation and testing and records nothing can more easily be found at fault if something goes wrong. If your particular product carries a manufacturer instruction to patch test, that should always be followed, as should the guidance to check for skin sensitivity before use.
Knowing a good practitioner
Green flags
A trustworthy salon is open about exactly which product it uses and will happily share the Safety Data Sheet and explain whether it contains or releases formaldehyde. Good practice includes a proper consultation that reviews your hair condition, previous chemical treatments and any health or scalp issues, along with a strand test where helpful. The treatment space should be well ventilated, with fans or extraction, and the stylist may wear a mask during the heat-sealing stage. Look for clear, honest advice about what the treatment can and cannot do, realistic estimates of how long results last, and detailed written aftercare. Experienced, trained stylists who are comfortable tailoring the finish to your hair, who follow the manufacturer's temperature and timing instructions, and who carry appropriate insurance are all reassuring signs of a responsible salon.
Red flags
Be cautious if a salon cannot or will not tell you which product they use or provide its Safety Data Sheet, or dismisses your questions about formaldehyde. A poorly ventilated, stuffy room with no extraction, and no willingness to open windows or use fans during the flat-ironing stage, is a warning sign, as is a strong chemical smell that makes your eyes water or throat sting while the stylist offers no protection. Treatments marketed as completely safe with no possible downsides, or pushed on you during pregnancy without caution, should raise doubt. Other concerns include no consultation or strand test, no questions about your medical history or previous chemical services, pressure to book on the spot, and prices that seem too good to be true. Trust your instincts and leave if you feel unwell.
Questions to ask
- Which specific smoothing product do you use, and can I see its Safety Data Sheet?
- Does it contain or release formaldehyde when heated, and if not, what is the active ingredient instead?
- How is the room ventilated during the flat-ironing stage?
- Will you do a consultation and a strand test to check how my hair will respond?
- Is this treatment suitable given my hair history, and is there any reason I should avoid it?
- How long should the results last for my hair type, and what aftercare do I need to follow?
Ready to book
Frequently asked questions
Is a keratin treatment or Brazilian Blowout safe?
It can be, but the main concern is formaldehyde, which some products release as a gas when heated and which is an irritant and a carcinogen at higher levels or with repeated exposure. Choosing a transparent salon, a lower-risk or formaldehyde-free product and a well-ventilated room greatly reduces the risk. Ask to see the Safety Data Sheet, and speak to a GP if you have any health concerns.
Does it permanently straighten my hair?
No. These treatments smooth the hair, reduce frizz and make it easier to style, but they do not permanently change your curl pattern. The effect is temporary and typically fades over three to six months as it washes out, after which your natural texture returns.
Can I have it done while pregnant or breastfeeding?
Many salons and product makers advise against it as a precaution, mainly because of possible formaldehyde exposure. If you are pregnant or breastfeeding it is best to discuss it with your midwife or GP before booking rather than relying on the salon alone.
What does formaldehyde-free actually mean?
It usually means the product uses alternative ingredients such as glyoxylic acid, carbocysteine or amino acids instead of formaldehyde or formalin. This is generally lower risk, but some of these can still release small amounts of formaldehyde when heated, so good ventilation still matters and you should still ask what is in the product.
How do I make the results last longer?
Follow the aftercare carefully, especially any instruction to keep hair dry and loose for the first few days. Use sulphate-free and salt-free shampoo and conditioner, wash less often, and protect your hair from chlorine, salt water and strong sun, all of which help preserve the smoothing effect.
This guide is general information, not medical advice. Speak to a qualified practitioner, and to your GP if you have a medical condition, before booking.