Hair removal definitions

Hair removal: definitions

Before we get going, I need to define some terms as they’re used in this discussion. It turns out that in the hair removal industry, results aren’t the only thing that can be confusing. So let’s get precise!


This might sound silly, but hair needs to be defined. When some people say that their device removes hair, they don’t always mean that it removes every type of hair. In fact, it’s not possible to remove every type of hair in an area permanently in one treatment. The following are distilled from an excellent summary of the basics [1].

There are three types of hairs you might see on your skin:

  • Vellus: sometimes called “peach fuzz,” these are tiny colorless hairs.
  • Intermediate: hairs between vellus and terminal. Thin, but with some pigmentation.
  • Terminal: these are deep-rooted coarse hairs, either pigmented or gray (usually the hairs consumers want removed).

In addition, all hairs have a three-stage growth cycle:

  • Anagen: active growing phase
  • Catagen: a brief transitional phase
  • Telogen: dormant phase until shed and replaced by a new anagen hair

The amounts of each type of hair and hair growth-cycles vary from person to person. That’s another reason why it’s tough to compare hair removal results between you and others. Depending on the body area, anywhere from 20% to 85% of hairs are in anagen (this is called the anagen/telogen ratio). Many hair-removal methods have been shown to be more effective on actively growing anagen hair. That means that a single treatment from a device cannot treat all your hairs.

One last thing to discuss is potential follicles. Many follicles do not produce a hair, even though they have the potential to do so. Follicles can be activated by hormonal changes (like puberty, pregnancy, aging, etc.) or by other chemicals or medical conditions. That’s why even after permanent hair removal, totally new hairs may grow.

“Permanent hair removal”

Most consumers assume “permanent” means lasting forever. Unfortunately, that’s not always the case as it’s used in advertising. For instance, a permanent wave in your hair is not really permanent.

How much time should elapse before results can be considered permanent? Since waiting forever is out of the question, many people, myself included, have suggested arbitrary definitions of “permanent” when assessing new hair-removal devices. Some of the definitions people use are pretty silly. One manufacturer claims its device is permanent based on results after 9 weeks. It’s ridiculous to base a claim on such a short period of observation., but the FDA formerly permitted this to be done [2]. Waxing can last that long, and it’s been clinically observed to be temporary [3].

Permanent hair removal can be generally defined as “the complete destruction of a treated hair follicle’s ability to generate hair.” Here’s my personal and unofficial working definition of “permanent hair removal” when assessing new devices:

Able to go one year after your final hair removal treatment and still be as clear of hair in the treated area as you were right after your final treatment.

This, of course, also means you went a year without having to use any other method to remove or conceal hair in the treated area.

This is based in part on one definition for permanent hair reduction (below). However, some hairs have a growth cycle lasting several years [1]. That means a year might not be long enough to determine true permanence, but a lot of consumers would be happy to have one hair-removal treatment a year.

Permanent hair reduction”

Another confusing definition. In 1998, the US Food and Drug Administration (FDA) began allowing some manufacturers of hair removal lasers and flash lamps used for epilation to use the term “permanent hair reduction,” [4] which the agency defines as:

The long-term, stable reduction in the number of hairs regrowing after a treatment regime. The number of hairs regrowing must be stable over a time greater than the duration of the complete growth cycle of hair follicles, which varies from 4-12 months according to body location. Permanent hair reduction does not necessarily imply the elimination of all hairs in the treatment area.[5]

For clearance purposes, FDA requires that hair counts be measured at 3, 6, 9, and 12 months following the last treatment [5].

This is one of those complicated things I warned you about! I’ll explain “permanent hair reduction” in detail in the section on laser hair removal.

“Response rate”

Defined here as: the percentage of people who respond to treatment.

Medical literature indicates that, for unknown reasons, some consumers don’t respond to laser or electrolysis procedures [6,7]. The less clinical data available, the higher the margin of error in the response rate. With Vaniqa, for example, 58% of women responded to the active ingredient [8]. However, if one-third of the subjects were “false positives” as they were in the control group, the actual response rate would really be closer to 25%.That’s why you can’t rely on the personal experiences of a few people. Response rates must be compared against a large control group to determine that positive results aren’t just coincidence, since we’re dealing with so many variables.

“Regrowth rate”

Defined here as: the percentage of hair that returns following one or several treatments.

Medical literature indicates that regrowth rates following hair removal vary wildly. This means regrowth rates are virtually impossible to estimate accurately. For instance, from 22% to 100% regrowth has been reported in long-term laser treatment follow-up [9,10]. Even after 125 years of clinical and empirical evidence regarding electrolysis, published estimates still range between 15% to 50%.[11]. Another expert can only estimate regrowth might range from 20% to 30% per treatment under ideal conditions, adding “the exact percentage is unknown.” [12] The less clinical and empirical data available, the higher the margin of error in the regrowth rate for each method.

Also, what is counted as regrowth must be carefully defined. Appropriately rigorous studies should describe the total numbers of hairs treated, specifying the number of terminal and vellus hairs [13]. Some researchers have suggested a definition of regrowth which only counts terminal hairs.[14]. Although many consumers seeking treatment are primarily interested in removing terminal hairs, this selective definition of regrowth makes treatment results look better at first glance and obfuscates true efficacy rates.

Whew! Now that we’re all on the same page, let’s look at some of the devices and claims out there.


  1. Richards RN, Meharg GE. Cosmetic and Medical Electrolysis and Temporary Hair Removal: A practice manual and reference guide. Toronto: Medric Ltd.,1991, pp 37-40.
  2. FDA Docket K892514, Aug 8, 1990. Following several failed submissions rejected by FDA reviewer Theodore Stevens, electric tweezer maker AHRS submitted an unpublished in-house report on 5 subjects followed for 9 weeks. The new FDA reviewer, Paul Tilton, allowed 9 weeks as a performance standard for permanent hair removal. Subsequently, AHRS (and a clone called GHR, which Tilton cleared in 1991) can claim they are “permanent.” The FDA subsequently set a more sensible performance standard and now requires 12 months of clinical follow-up for considering claims of permanent hair reduction. The FDA also stated in 1998 that there are no significant data to substantiate claims of electric tweezer permanence [Docket 97N-0199]. For an extensive critical analysis of the Tilton decision, you can download Docket 99P-1614. The Tilton decision is an unfortunate footnote in the history of hair-removal regulation and a triumph of quackery over good science.
  3. Richards RN, Uy M, Meharg G. Temporary hair removal in patients with hirsutism: A clinical study. Cutis 45:199-202, 1990.
  4. FDA Docket K980517. July 21, 1998. See summary (requires Adobe Acrobat).
  5. Richard Felten, personal correspondence, 17 April 2001.
  6. Liew SH and others. The effect of ruby laser light on cellular proliferation of epidermal cells. Annals of Plastic Surgery 43:519-522, 1999.
  7. Richards RN, Meharg GE. Electrolysis: Observations from 13 years and 140,000 hours of experience. Journal of the American Academy of Dermatology 33:662-666, 1995.
  8. Vaniqa package insert. VaniqaTM is a trademark of Bristol-Myers Squibb Company.
  9. Lloyd JR, Mirkov M. Long-term evaluation of the long-pulsed alexandrite laser for the removal of bikini hair at shortened treatment intervals. Dermatologic Surgery 226:633-637, 2000.
  10. Nanni CA, Alster TS. Optimizing treatment parameters for hair removal using a topical carbon-based solution and 1064-nm Q-switched neodymium:YAG laser energy. Archives of Dermatology 133:1546-1549, 1997.
  11. Richards (1991), p. 248
  12. Wagner RF Jr, Tomich JM, Grande DJ. Electrolysis and thermolysis for permanent hair removal. Journal of the American Academy of Dermatology 12:441-449, 1985.
  13. Kobayashi T. Electrosurgery using insulated needles: Epilation. Journal of Dermatologic Surgery and Oncology11:993-1000, 1985.
  14. Grossman MC and others. Damage to hair follicles by normal-mode ruby laser pulses. Journal of the American Academy of Dermatology 35:889-894, 1996

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