Keratin straightening. The complete guide.

Keratin is the protein hair is built from. Keratin straightening returns it to the hair and seals it in with heat. Here is everything worth knowing before you book.

By the HER BOSS teamUpdated: September 2026Reading time: about 5 minutes

What keratin straightening is

Keratin is the protein hair is made of. About 90% of a strand's weight is keratin, and it is what gives the strand its strength, elasticity and structure. Colour, heat, sun and hot water open gaps in the keratin, and those gaps are why hair looks frizzy, dry and dull.

Keratin straightening is a treatment in which a formula rich in keratin broken down into small particles is applied to the hair, given time to absorb, and then sealed inside the strand with the controlled heat of a flat iron. The keratin fills the gaps and the strand becomes full, straight and smooth again.

Unlike Japanese straightening, keratin straightening does not break the chemical bonds of the hair strand. It builds on what is there. That is why it also suits hair that has been coloured, lightened or previously straightened, and when done correctly it repairs rather than only straightens.

How the treatment works, step by step

1. Diagnosis. The stylist checks the hair type, its condition and its history: colour, lightening, previous straightening. This is the stage that sets the processing time and the heat.
2. Clarifying wash. A cuticle-opening shampoo that removes silicone and styling product residue, so the formula gets into the strand instead of sitting on it.
3. Application. The formula is applied strand by strand, from root to ends, and stays on the hair for the processing time set during the diagnosis.
4. Drying and flat iron. The hair is dried and straightened with a professional flat iron at a controlled temperature. The heat seals the keratin inside the strand. This is the stage that turns absorption into a result that lasts.
5. Finish. Under the Herboss straightening protocol the hair is washed in the salon right at the end, with salt-free shampoo and mask. You leave with clean hair, with no days of waiting.

A full treatment takes four to five hours, depending on the length and thickness of the hair.

Who keratin straightening suits

• Frizzy and wavy hair that wants to be smooth without drying out.
• Coloured or bleached hair. This is one of the situations where repair with protein makes the biggest difference. On heavily bleached hair a strand test is done first.
• Fine and thin hair. The formula fills the strand and gives it body, provided the processing time and heat are adjusted.
• Thick and afro hair. Needs a longer processing time and precise heat, which is why it matters that the stylist has been trained on the product.

When not: during pregnancy and breastfeeding our recommendation is to wait (full explanation here), and on an injured or irritated scalp you wait for it to heal.

Keratin alone, or keratin and collagen

Most straightening products on the market rely on a single protein. One protein can straighten or soften, not both. That is why quite a few clients know the result of smooth hair that feels like straw.

Herboss straightening has two proteins in one formula: keratin rebuilds the framework that holds the strand straight, and collagen seals the cuticle over it. The softness and shine come from the collagen, from the strand itself and not from a silicone coating that comes off by the third shampoo. More on collagen.

How long keratin straightening lasts

Regular keratin straightening usually lasts three to five months and fades gradually with every wash. With Herboss straightening the treated hair stays smooth and does not go back to frizz: what grows back from the root is natural hair, and that is what gets treated next time. The only thing that varies from client to client is how often the new root growth needs treating.

What extends the result: salt-free shampoo and mask, water that is not very hot, and a flat iron only when needed. The aftercare guide.

What about formaldehyde

In the early years of Brazilian straightening, formaldehyde was used to fix the keratin. Formaldehyde is released as a gas when heated and is hazardous to breathe, so its use in cosmetics is restricted by regulation. Some formulas replaced it with glyoxylic acid, about which worrying medical reports have also accumulated in recent years.

Herboss straightening is free of formaldehyde and glyoxylic acid, and is registered with the Israeli Ministry of Health under number 0892026113912. How to check a product before straightening.

What the diagnosis checks, and why it decides everything

A good diagnosis takes ten minutes and prevents months of disappointment. A trained stylist checks four things:

• Porosity. How quickly the strand absorbs water. Porous hair (usually coloured or bleached) absorbs the formula quickly and needs a shorter processing time and lower heat.
• Elasticity. A wet strand that stretches and springs back is healthy hair. A strand that snaps or stays stretched is hair that needs repair before straightening.
• History. Colour, lightening, previous straightening, and exactly what was in them. A past Japanese straightening changes the protocol.
• Scalp. Wounds, irritation or active psoriasis: wait until they settle.

On heavily bleached hair a strand test is also done: one hidden strand is treated, and you see how it reacts before doing the whole head.

Marketing names worth knowing

• Brazilian straightening. The original name for keratin straightening, from the time when formaldehyde was still used. Today it is used for almost any protein straightening.
• Hair botox. There is no botox in it. It is a deep conditioning treatment that softens and adds shine, and usually does not straighten. Suits anyone who wants repair without straightening.
• Nano keratin, silk keratin, gold keratin. Marketing add-ons to the same idea: protein sealed in with heat. What matters is the ingredients and the registration, not the label.
• Collagen straightening. Collagen alone softens and seals but does not build the structure that holds the strand straight. Full explanation.

Mistakes that shorten the life of a straightening

1. Shampoo with salts. Salts open the cuticle and wash out what the straightening sealed in. This is the number one reason straightening "goes" after a month.
2. Very hot water. Heat in water does the same thing. Lukewarm.
3. Sea and pool without preparation. Salt and chlorine dry hair out. Wet your hair with fresh water and apply serum before, rinse after.
4. A flat iron every morning. Smooth hair does not need it. When it does, low heat.
5. Shortening the processing time in the salon. The processing time is what holds the result. Anyone who promises straightening in an hour is skipping it.

The complete guide to aftercare.

Keratin straightening for men, teenage girls and grey hair

Men. The same protocol, usually with a shorter treatment time because of the length. Especially suited to frizzy hair that is hard to manage.

Teenage girls. We recommend waiting until age 16 or older, and in any case with a parent at the diagnosis. Young hair usually does not need structural straightening, and sometimes repair is enough.

Grey and white hair. Suitable. Grey hair tends to be dry and porous, which is exactly why it benefits from collagen. With Herboss straightening the colour does not change or turn yellow.

How to spot a salon that knows how to work with keratin

• She asks about the hair's history before she names a price.
• She can tell you the product's registration number and what is and is not in it.
• She does a strand test on bleached hair, even if it causes a delay.
• She explains what happens at the end: a wash in the salon or days of waiting.
• She does not promise "forever" without saying that the root growing in is natural hair.

Salons trained in Herboss straightening are listed on the map of certified salons.

How much keratin straightening costs

In Israel the price of keratin straightening in a salon usually ranges from 500 to 1,500 shekels, depending on the hair's length, thickness and condition, the type of product and the stylist's experience. A quality product, a proper diagnosis and four hours of treatment time account for most of the difference between the low price and the high one. What sets the price, in detail.

Frequently asked questions