Permanent hair straightening treatments are a form of chemical processing for your hair. Depending on what method of processing you use, hair that’s naturally curly or textured can be altered to lay flat and lose its curl.

These treatments work for several months or more, usually lasting until new hair grows in to replace the hair that was treated. For this reason, these processes are called permanent hair straightening.

The “permanent hair straightening” label can be used to refer to keratin treatments, thermal straightening, and “perm” straightening processes. If you find your wavy or curly hair hard to style or just want a change in your look, these processes can be appealing.

Self at-home treatments and salon treatments are both popular options. This article will help you be informed about the pros and cons of this kind of hair treatment.

There are several types of treatments that claim to make your hair straighter. Each relies on a different chemical formula and processing method. Some of these treatments are sold in kits that you can do yourself at home, while others require salon-grade equipment to be done effectively.

Professional permanent straightening

A perm refers to a chemical process that permanently alters the hair follicle. Perms are sometimes associated with creating curls in hair that doesn’t naturally have it, but they can be used to make hair straight, too.

Perms are usually done in one appointment that takes a few hours. The cost of a perm can vary according to your salon and how long your hair is. Typically, prices start around $50.

At-home perms

Chemical relaxant kits can be purchased at pharmacies and beauty supply stores. These treatments claim to offer the same results as a perm from a salon. Unless you have formal cosmetology training, it will be tricky to use these kits effectively. At-home perm options tend to start around $15.

Semi-permanent hair straightening

Keratin hair treatments, Brazilian blowouts, and semi-permanent hair straightening all refer to a method of treating your hair for a straight texture that lasts 3 to 5 months. This method can take multiple salon appointments to finish application, and typically costs over $150.

Thermal straightening

Japanese thermal hair straightening, also called an acid perm, is more similar to a traditional “straight” perm than it is to a keratin treatment.

This process might involve the longest time spent in a salon chair (5 to 6 hours), but it also claims to last the longest (up to 6 months). It also costs the most, ranging from $200 to $800.

All permanent hair straightening methods use the same strategy.

A chemical solution is applied to your hair. These chemicals change the way that the proteins in your hair are configured.

With perms and thermal straightening procedures, a neutralizer is then applied to your hair. This neutralizer causes your hair to lock into its new shape, with new bonds forming between the protein molecules of your hair.

It can take several hours to infuse the hair with the chemical solution, apply the neutralizer, and style your hair. These chemical solutions often carry strong scents, and in many cases you’re cautioned against getting your hair wet or even sweating too much in the days following the treatment.

This means that you’re walking around inhaling the chemicals used to treat your hair, as well as exposing everyone near you to them.

Hair breakage after a permanent hair straightening treatment is somewhat common. The chemical solution works by, in essence, damaging your hair so it lies flat or releases its natural curl.

This means that your hair may be harder to style and take longer to dry until it grows out and new, untreated hair takes its place.

There’s also a concern about the chemicals used for these straightening processes.

Formaldehyde, which is in almost all straightening solutions, is a known carcinogen. Applying it to your hair and inhaling fumes causes exposure strong enough to cause side effects. These may include respiratory difficulties, irritation to your nose and eyes, and skin redness and irritation.

What about natural products?

Even “all-natural” or “formaldehyde-free” formulas of hair straighteners are often full of duplicate chemicals that become formaldehyde when they’re heated.

A 2014 study on Brazilian keratin hair straightening treatments found formaldehyde levels that were deemed high enough to pose a health hazard for consumers.

Of course, it’s better for your health to look for low-exposure options, but this is a case where reading the labels and asking questions won’t necessarily yield the truth about the product you’re using.

According to the Environmental Working Group, chemical straighteners that are lye-free or alkaline sulfite-based are safer than some alternatives. Of course, the safest option of all is to avoid exposure to harmful chemicals that can absorb through your scalp and your nasal passages.

You shouldn’t get any of these permanent straightening treatments if you’re pregnant or trying to become pregnant.

The pros and cons of each hair straightening depend on what method you’re considering.

Permanent hair straightening

At-home perms

Keratin treatments

Thermal straightening

Semi-permanent hair straightening lasts 3 to 4 months before your natural hair texture starts to reappear.

Home hair straightening kits don’t often last longer than 6 weeks.

Permanent hair straightening done in a salon lasts anywhere from 4 to 6 months. Once your roots start to grow in, you’ll need to decide if you’re going to repeat the treatment or wait for it to grow out completely.

Permanent hair straightening refers to treatments that will make your hair straight beyond a wash or two. Beyond that vague definition, your results will vary widely according to your hair type, how quickly it grows, and the chemical method you use to straighten your hair.

Keep in mind that “permanent” doesn’t mean forever — it just refers to the duration of one life cycle of your hair. Speak to your hairstylist about your options, and what they think might be the best one for you.