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Women who have thick hair usually have no problem perming if they want. Gals with thin hair, on the other hand, have to be careful with perms to keep their hair healthy and as full as possible. No one wants her already-thin hair to break or fall out. Going for a gentle perm is usually the best option, with acid perms winning out over other perm types.
Thin hair means you don't have a lot of hair strands on your head. Lots of people misuse this term and say it when they really mean hair has a smaller diameter, or that the hair is fine. When your hair is thin, you can't afford a lot of damage and breakage. Those issues thin out your hair even more and end up robbing you of volume.
Your Choices and the Pick
When you pop into the salon chair for a perm, your stylist has three main options. These include alkaline, acid-balanced and acid perms. The main chemical in the alkaline type is ammonium thioglycolate; these perms have a pH level of around 9 to 9.6. Acid-balanced and acid perms use glyceryl monothioglycolate. Acid-balanced perms have pH levels somewhere between 7.8 and 8.2 -- they produce firmer waves the way alkaline perms do, but are gentler. Acid perms have the lowest pH, usually around 4.5 to 7. That said, acid perms tend to be gentlest and do the least damage, simply because their pH doesn't give them quite as much oomph as the other two perm types. Thin hair needs all the TLC you can give it, so the gentler the perm you can get, the better. Acid perms usually are the best option for thin hair unless your hair gets snobbish and won't respond to perms with a lower pH.
Stylists typically know half a dozen to a dozen different types of perm styles. These are all based on how they roll your hair on the rods and how much hair they work with. Sometimes a root perm is the best option for a thin-haired gal because it only affects the hair near the scalp. This means you can get some lift and make your hair look fuller without damaging the rest of your tresses. On the other hand, thin hair typically needs some help in the volume department. If your hair is both fine and thin, you might like a stack or spiral perm. Spiral perms give all-over results and lots of body, but because your stylist goes to work rolling the hair vertically, they don't look quite as big or layered as a horizontally-rolled stack perm does. If you want body but also want a very natural-looking style, a beach wave style can work.
Acid perms are good choices for thin hair because they're less damaging to your strands. At the same time, this gentleness comes with a tradeoff. Acid perms don't have the power to produce curls or waves that look firm and tight. Instead, they give looser, more flexible results. This is usually a good thing because flexible hair looks really natural, but it also means your perm isn't going to last quite as long. Whereas most perms last between two and six months, acid perms tend to fall at the shorter end of that range.