Editor's note:
Summer is here, and everyone's clothes are getting scarcer. "kiwi" boys and girls have reached the most difficult season of the year again. As two-legged beasts that evolved from monkeys, the existence of body hair provides us with a lot of conveniences, but it also brings many problems. Throughout history, starting from " ancient Egypt ", people have studied various hair removal methods. Techniques have developed into modern times. Folk remedies, hair removal beeswax , medical aesthetic lasers and other hair removal methods have emerged in endlessly, which is dazzling. Today, let us explore "the little thing of hair removal" with a professional dermatologist.
1 Let’s start with hair.
There are about “5 million” hair follicles in the human body, and about “1 million” in the scalp. They are mainly divided into three categories: fetal vellus hair, adult vellus hair and terminal hair. Vellus hair is what we often see. Talk about "body hair".
Terminal hair is divided into long hair and short hair. Long hair such as hair, beard, pubic hair, armpit hair, short hair such as eyebrows, eyelashes, nose hair, etc.
These three types of hair follicles all follow the same hair follicle growth cycle, including the growth phase, the regression phase and the resting phase. Most of the hairs that can be seen by the naked eye are in the growth phase.
The growth cycle of hair
*From left to right: anagen, catagen, telogen, and the next growth phase
Image source: William Daniel. Andrews' Diseases of the skin: clinical dermatology.11th ed. Elsevier 2011.P7
Whether body hair is thick or sparse is mainly determined by genetic factors. Of course, it is also affected by acquired factors, such as endocrine, nerve, blood vessel, nutrition and other factors that may cause changes in body hair density. The increase of androgen in the body before and after puberty may cause the increase and thickening of body hair. Certain chronic inflammatory stimuli may also cause abnormal increase in hair in local inflammatory areas.
2 Daily Hair Removal Tips
Choosing a hair removal method should be based on specific needs. If you just need your skin to look clean on a certain occasion, choosing a multi-layered blade "shaving razor" to remove excess hair is the fastest and easiest way to remove hair without much damage to the hair or skin.
However, shaving can only make the hair shorter. If you want the skin to remain smooth and clean, you need to repeat the operation regularly, and there is a risk of scratching the skin and causing infection.
Women's Shaving Knife (picture reproduced and deleted)
If it only targets the increase of hair in a small area, such as unibrow, "hair removal" may be an option. After the hair in the growth phase is removed, it takes 6-8 weeks for new hair to gradually replace it, so the effect can last for nearly 2 months. However, direct hair removal methods such as tweezers are painful and time-consuming. For body hair with a slightly larger area, electric hair pullers or adhesive removal methods such as glue, beeswax, , etc. can be used to increase the efficiency of body hair removal, which is called "Physical hair removal" , this type of hair removal method is simple, convenient and low-cost, but it is also painful, can easily lead to complications such as folliculitis and scars , and generally hair will gradually resume growth after 2 months.
"There is always a hair-plucking tweezer that suits you" (picture reproduced and deleted)
Chemical hair removal mainly uses the thioglycolate in "hair removal cream" to destroy the disulfide bonds in the hair and dissolve the hair shaft structure, so as to achieve the hair removal effect, it can be said to be the upgraded version of shaving hair . The hair removal agent is very effective in removing most body hair, but because it only destroys the hair shaft rather than the hair follicle, the hair removal effect is difficult to last for more than 2 weeks. Since most hair removers are sulfur-containing compounds, the smell is relatively unpleasant, and some sensitive skin can also induce contact dermatitis or even post-inflammatory pigmentation . You need to try it on a small area first.
Hair Removal Cream (picture reproduced and deleted)
3 Medical and aesthetic hair removal
Among medical and aesthetic hair removal, the effect of laser hair removal is generally close to permanent, and it is also safer. It is currently the most widely used.Its principle is to use "selective photothermal effect" to allow laser of a specific wavelength to penetrate but not burn the epidermis. The melanin in the hair follicles during the growth period selectively absorbs the laser energy, causing "heated coagulation and necrosis of hair follicles" , thereby achieving the effect of permanent hair removal.
In practical applications, cooling is often applied to the skin surface to increase the comfort of the treatment process. "Low-end version" hair removal equipment can also choose intense pulsed light (photon) hair removal or household handheld hair removal equipment, but due to its relatively low power, the effect is worse than medical equipment.
The laser wavelength absorption coefficient corresponding to different target color groups in the skin
*Melanin (shown as blue line) selectively absorbs light energy around 600-800nm wavelength and is stronger than hemoglobin, fat and water
Picture quoted from: Bolognia, JL et al. (2018) Dermatology. 4th ed. Elsevier. P2356.
Since hair in the growth phase only accounts for a fixed proportion of the total number of hairs, laser hair removal usually needs to be repeated repeatedly to achieve the ideal hair removal effect.
Taking the currently commonly used 755nm alexandrite laser hair removal machine as an example, the treatment is usually repeated once every 1-2 months, and most require more than 3-5 times to achieve a permanent hair reduction of 70%-80%. A small number of people may also need maintenance treatment every 6-12 months to remove the fine vellus hair that has regrown.
The wavelengths and penetration depths of different types of lasers in the skin
(corresponding to the depth of hair follicles on the right side)
Left: Bolognia, JL et al. (2018) Dermatology. 4th ed. Elsevier. P2357. Right: William Daniel. Andrews' Diseases of the skin: clinical dermatology.11th ed. Elsevier 2011.P7.
Of course, the cost of laser hair removal is also higher than that of other hair removal methods, and short-term pain and short-term pain may also occur after treatment. Transient discomfort such as edema around the hair follicles and erythema can mostly be relieved by cold compress or gel dressing.
4 written at the back
In short, if you want to get it done once and for all, it is recommended to choose "Laser Hair Removal" . If you want to spend less and have better skin tolerance, you can choose "physical hair removal" or "chemical hair removal" . If hair needs to be removed only for a short period of time, shaving is still the easiest, fastest and safest method.
No matter which hair removal method you choose, you must remind your friends that you must do good skin care after hair removal, keep the local area clean and hygienic , take gentle care of the skin and strictly protect yourself from the sun to avoid aggravating skin irritation and sensitivity. It can even lead to complications such as infection, pigmentation and scarring.
Of course, the above is mainly for body hair and armpit hair removal methods. As for the hair removal method for long hair, it should be relatively simple...
Reference:
1. Original work by JL Bolognia and others, translated by Zhu Xuejun and others. Dermatology (4th edition). Peking University Medical Press, November 2019. P1265-1278.
2. Edited by DW Shenenberger, translated by Sun Ling, Removal of unwanted hair. UpToDate clinical consultant. Topic last updated date: 2022-05-09.
Author: Beijing Shu Chang, attending physician at the Department of Dermatology, Union Medical College Hospital
Editor: Random Thoughts Bubble Da Lun Shi Hong
Daily question to identify diseases with a smart eye
Selected daily question
The physical signs shown in the picture below are:
Swipe down to see the answer
Answer: Positive Trendelenburg sign, congenital hip dislocation
Analysis: Trendelenburg sign is also called one-legged standing test. Under normal circumstances, the gluteus medius muscle contracts and the contralateral pelvis lifts; in the picture, the left side of the patient has congenital hip dislocation. When the side is weight-bearing, the gluteus medius and minimus relax, the contralateral pelvis does not rise but falls, and the trunk tilts to the left, which is called a positive Trendelenburg sign.
Question source: Previous clinical physician qualification examination real questions
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