Relaxers: No-Lye vs. Lye explained

Relaxers usually refer to the lotions or creams used to straighten tight curls by chemically ‘relaxing’ the natural curls. The active agent used to be mainly a strong alkali such as sodium hydroxide (lye) but nowadays there are several options in the no-lye category. Let’s take a look at the differences between the lye and no-lye relaxers.

Lye relaxers

The principle of relaxing hair requires an alkaline solution to penetrate the cortex of the hair, and to disrupt the internal protein bonds/interactions within the hair fiber and therefore modify the physical structure of the hair. In this case we are referring to changing the hair from curly to straight.

A lye relaxer consists of sodium hydroxide also referred to as lye (chemical formula: NaOH ) mixed with water, petroleum jelly, mineral oil, and emulsifiers to create a creamy consistency. The cream is applied and allowed to sit on the hair for 15–20 minutes (depending on brand). Hair is then shampooed and conditioned as in the normal routine, and styled straight.

The pH is usually between 10 and 14. This high pH is what causes the hair to swell for the cream to permeate the hair fiber.

No-lye relaxers

Because of increasing awareness of the potential dangers of sodium hydroxide found in traditional relaxer formulas, many women have begun abandoning them. Indeed because lye relaxers are efficient in changing the internal structure of hair, it also implies that it can do more damage to the core of the hair fiber. But more importantly, misuse of this product has resulted in scalp irritations, hair loss and other problems. Thus the no-lye relaxers have become more popular.

In one version of the no-lye relaxers, the alkali (or base) used is usually milder than sodium hydroxide and thus safer. The three main hydroxide bases used: potassium hydroxide, lithium hydroxide, or guanidine hydroxide. Note that guanidine hydroxide is not present (pre-formulated) as such in the kit but instead the relaxer packaging will contain a cream containing calcium hydroxide (slaked lime) with an “activating solution” of guanidine carbonate. The combination of these two ingredients will thus produce the required guanidine hydroxide.

Another type of no-lye relaxer uses ammonium thioglycolate, which is also known for its use in perming or even in Japanese hair straightening in the salons. The ammonium thioglycolate is a reducing agent which selectively breaks the hair’s cystine bonds instead of disrupting the entire hair protein. It is therefore less aggressive to hair in that aspect compared to the hydroxide bases.

At the end of the reducing process, the thioglycolate must be oxidized with a special solution of hydrogen peroxide or sodium bromate to reform the cystine bonds in the straightened hair. See here for Japanese hair straightening. The example below shows the ingredients in a no-lye relaxer kit containing ammonium thioglycolate.

Lastly,no-lye relaxers in home kits also contain the active agents: ammonium sulfite and ammonium bisulfite (the two compounds are interchangeable, depending on the surrounding pH). These work similarly to ammonium thioglycolate but are much weaker and work more slowly. Their mild action therefore also minimizes (but does not entirely eliminate) hair damage as well as collateral irritation to the skin.

Word of caution

Sometimes, the relaxers do not seem to work as well as expected, and it is tempting to retry the process again. Bear in mind, that doing a repeated process can ruin the integrity of your hair due to the significant damage that will be inflicted by 2 consecutive treatments. Additionally, it is advised to stay away from hair coloring or other chemical treatment after the hair has been straightened. Again, it’s to avoid the risk of severely breaking/damaging the fibers.


Originally published at on November 6, 2015.

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