Relaxing is a chemical process that puts your tresses through a shape metamorphosis, taking out some of the curl or wave you have. Generally, this is something ladies with thicker hair do to get better manageability or a sleeker look, but it might be something you still need with thin hair if your tresses are unruly. If your hair is thin, you have to pick relaxers that won't make the thinness worse.
What "Thin" Means
Although "thin" can seem pretty straightforward when you're talking about your hair, it's a term that's widely misused. Thinness has nothing to do with the circumference or diameter of your hair. If your stylist is talking about these factors, he's talking about whether your hair is coarse or fine. Thinness refers to hair density, or how many hairs you've got on your scalp. The best relaxer for you, therefore, might not be the same one your best gal pal needs.
Types of Relaxers
Relaxers come in three major flavors: lye, no-lye and ammonium thioglycolate. Lye relaxers transform your tresses with sodium hydroxide. These relaxers mean serious business and generally have a pH level in the neighborhood of 12 to 14. Some lye relaxers are formulated with a lower concentration of sodium hydroxide, so they're a little gentler. No-lye relaxers still have hydroxides, such as lithium, potassium or calcium hydroxide. These are still tough with a pH of 9 to11. Ammonium thioglycolate is the ammonium salt of thioglycolic acid. It's better known as perm salt. Ammonium thioglycolate relaxers often are the gentlest with a pH of around 10.
Because you don't have a lot of strands to lose when your hair is thinning, you want to pick the gentlest relaxer that will do the job so that you keep damage and subsequent breakage to a minimum. A no-lye relaxer can have a pH similar to an ammonium thioglycolate relaxer. Both break down the disulfide bonds deep in your hair strands that help give your hair its shape. A disulfide bond is just one of the four types of bonds in your hair; technically defined, it is the chemical link between the sulfur atoms of two cysteine amino acids. No-lye relaxers don't repair these bonds, however. Ammonium thioglycolate relaxers, by comparison, use a neutralizer that puts some of the bonds back together. The translation for your hair is that no-lye relaxers often make your hair weaker than ammonium thioglycolate ones. Because ammonium thioglycolate relaxers work in this way and are gentler than others because of their lower pH, they usually are the best pick for thin hair, unless you've got particularly stubborn locks.
Some ladies with thin hair have very sensitive scalps. Even if your hair is very stubborn, this can make it impossible for you to use a very alkaline sodium-hydroxide relaxer. In this case, no-lye relaxers can be better. They're stronger than the ammonium thioglycolate relaxers and thus have the power to bully your hair into responding, but the lower pH compared to lye relaxers causes less skin irritation. Another important issue is that thioglycolate and hydroxides are not compatible. If you mix the two, you can chemically burn off your hair. The best relaxer for you thus depends in part on what you've previously done to your mane. If you've previously permed it to give your thinning strands some volume, you likely will need an ammonium thioglycolate relaxer by default, because the chemical in a standard alkaline perm is ammonium thioglycolate.