Prepubertal hypertrichosis

There is limited research available to fully understand the pathophysiology of prepubertal hypertrichosis and mechanism of hair growth in this condition, but a potential pathway in some is attributed to increased concentrations of testosterone in the body.[2] The elevated testosterone levels can lead to excessive hair growth all over the body during childhood, with the most affected areas being the face, back, and areas closer to the trunk of the body.[2] Although the mechanism is not yet clear, some medications can cause hypertrichosis.[14] Minoxidil and cyclosporine are some examples of medications that can cause hypertrichosis.[14]

There is no clear identifiable cause for most cases of prepubertal hypertrichosis.[4] Prepubertal hypertrichosis may be due to genetics, systemic illnesses, or medications.[3][4]

Listed below are some genetic syndromes that are currently known to cause hypertrichosis:[2]

• Zimmermann–Laband syndrome
• Coffin–Siris syndrome
• Schnizel–Giedion midface retraction syndrome
• Gorlin–Chaudry Moss syndrome
• Adducted thumbs syndrome
• Barber–Say syndrome

Listed below are some systemic illnesses that are currently known to cause hypertrichosis:[2]

• Thyroid hormone level abnormality
• Malnutrition
• Cancer

Listed below are some medications that are currently known to cause hypertrichosis:[2]

• Minoxidil
• Cyclosporine
• Diazoxide
• Danazol
• Phenothiazine
• Hydantoin
• Omeprazole - possibly via modulation of prostaglandin pathways responsible for hair growth and regulation.[15]

In addition, there are two prominent mechanisms that are currently being used to explain the development of hypertrichosis in individuals.[16]

The first proposed mechanism states that the excessive hair growth is due to the conversion of vellus hair (peach fuzz) to terminal hair (thick and dark).[16] This can be compared to terminal hair replacing vellus hair which occurs during puberty due to an increase in androgen production.[17][18] However the vellus to terminal hair conversion in hypertrichosis has yet to be fully understood.[16]

The second proposed mechanism involves the hair follicle growth cycle. Human hair follicles follow a growth cycle that has three stages: anagen, catagen, and telogen.[16] Active growth of the hair follicle occurs during the anagen phase. During the catagen phase, the hair follicle undergoes a process to prepare for hair shedding. The telogen phase is when hair shedding occurs. The hair follicle growth cycle varies by person and by body location of hair growth.[16] Hypertrichosis is said to occur when hair follicles are in the anagen phase longer than normal for their particular hair location.[16]

Despite the known mechanisms, there is currently little understanding as to what triggers them.[16]

Listed below are aspects that physicians take into consideration when determining the classification of hypertrichosis:[2]

• Which hair type is predominant
• Familial history of hypertrichosis
• Any evidence of a genetic syndrome that would cause hypertrichosis
• Current medication usage
• Thyroid hormone levels
• Nutritional status
• Cancer

• Lanugo hair: "fine, non-pigmented hair that covers the normal fetus. It is often several centimeters long. By the first few weeks of life, lanugo hair should be replaced by velds hair on the body and terminal hair on the scalp."[2]
• Vellus hair: "Lightly pigmented, fine, short hair, often referred to as "peach fuzz" that is found on the face, arms, stomach, and legs."[2]
• Terminal hair: "Coarse, thick hair that is found on the scalp, underarms, and pubic area."[2]

• Congenital: Present at the time of birth
• Acquired: Not present at the time of birth but develops sometime after birth

• Generalized: Not limited to a certain area
• Localized: Primarily affecting a certain area

Prepubertal hypertrichosis can be associated with other syndromes or diagnosed in isolation.[7] Isolated congenital generalized hypertrichosis includes monogenic disorders: hypertrichosis lanuginosa congenita and hypertrichosis congenita terminalis.[7] Syndromic congenital generalized hypertrichosis includes monogenic and chromosomal disorders.[7] The monogenic disorders may be further distinguished by autosomal dominant, autosomal recessive, and X-linked disorders.[7]

In 2020, a case study reported that a Caucasian child developed two patches of hypertrichosis at the sites of vaccine injection for Diphtheria-Tetanus-acellular Pertussis-poliovirus (DTPa-IPV) and chicken pox.[24] After the vaccines were given, the child had developed erythema, swelling, and itch at the two sites, and the hypertrichosis was reported 6 months later.[24]

Several case studies have reported hypertrichosis in children after the application of casts. One study done in 2012 identified a significant number of cases of hypertrichosis in a group of 117 patients, ages ranging from 3 to 91 years old after application of casts.[25]

The degree and type of management depends on the age of the child, the severity and location of the hypertrichosis, and the psychosocial needs of the child, their family, and society. The management strategies for controlling and removing the excessive hair growth include physical management strategies such as shaving, trimming, waxing, and tweezing, chemical strategies such as bleaching or use of chemical depilatories, the use of light sources in laser hair removal, intense pulse light therapy, and electrolysis.[5] More specifically, depilation temporarily removes hairs from the surface while epilation removes hairs from their bulb.[3] The management options vary in effectiveness, cost, and adverse effects such as pain, skin irritation, and distorted hair regrowth.[5]

Depilation methods include shaving and chemical depilatories. Shaving does not affect the growth rate or diameter of the individual hairs. However, it can appear thicker and more coarse than before due to the hair having a blunt tip after shaving.[26] While inexpensive, shaving can cause irritation, folliculitis, and ingrown hairs.[5][27] Chemical depilatories use sulfides, thioglycolates, or enzymatic depilatory agents which dissolve hairs by breaking the disulfide bonds in keratin which normally keep hair strong and healthy.[26] Chemical depilatories are painless and easy to use, coming in many forms such as powders, creams, and lotions. Sulfides are effective and work fast but can also produce hydrogen sulfide which has an unpleasant odor and can cause irritant contact dermatitis. Enzymatic depilatory agents do not produce an unpleasant odor and are nonirritating, but they also have not been found to be effective. Therefore, most chemical depilatories use thioglycolates. which work slower in comparison to sulfides but are less odiferous and irritating.[5]

Epilation methods include waxing, tweezing/plucking, laser hair removal, intense pulse light therapy, and electrolysis. Waxing is commonly used in larger areas and temporarily removes hair for about 2 to 6 weeks. Waxing can cause skin irritation, scars, folliculitis, and thermal injury due to the hot wax, and repeated waxing can reduce hair regrowth over time.[26] Tweezing or plucking hair is best for smaller areas and can remove hair for 2 to 12 weeks.[27] Tweezing is inexpensive and causes minimal skin damage, but it also takes the most time and can cause pain in sensitive areas.[26]

Laser hair removal uses red to near-infrared light (600-1100 nm) to remove hair. The light is absorbed by melanin in the hair which heats and damages the hair follicles to remove it. Laser hair removal has found to delay hair regrowth by up to 3 months.[28] Laser hair removal can cause redness, edema, first to second degree burns, skin damage, and pigmentation.[26] Those with darker skin types are at greater risk for dyspigmentation and scarring, because they have higher melanin content.[28]

Intense pulse light therapy (IPL) uses polychromatic light to cause permanent hair removal. The melanin found in hair absorbs these long wavelengths of light (590-900 nm) which are converted into heat to cause the destruction of the hair bulb to permanently remove the hair.[29] The choice of wavelength depends on a person's skin type and skin condition.[30] IPL is ideal for larger areas and can cause pain, edema, erythema, and pigmentation. While this option is less expensive than laser hair removal, it is also less effective and therefore, requires more treatment sessions.[26]

There are three different types of electrolysis: galvanic, thermolysis, and blend. Galvanic electrolysis uses a needle to directly deliver the electrical current to the hair follicle. The current has a corrosive effect, destroying the hair via production of sodium hydroxide.[5] While galvanic electrolysis is the more effective than thermolysis, it also is slower.[26] Thermolysis uses a high-frequency alternating current which produces heat to destroy the hair bulb. Thermolysis is less effective in thicker hairs and those with curved follicles.[5] Blend electrolysis combines both galvanic and thermolysis and is the most effective version of electrolysis. Electrolysis in general can cause pain, hyperpigmentation, and scarring, but galvanic electrolysis has the most severe of the side effects.[26]

Bleaching is an alternative management strategy. While bleaching does not remove hair or prevent is growth, it can lighten the appearance of hairs by removing the hair's natural pigment. The hydrogen peroxide in bleach helps to soften and oxidize the hairs to turn it into a yellowish hue. Bleaching is quick, easy, and painless, only causing some skin irritation. Additionally, the effects of bleaching can last up to 4 weeks.[5]

Eflornithine hydrochloride 13.9% cream (Vaniqa®) is a topical prescription medication that has been approved by the FDA as a treatment to reduce hair growth.[31] Eflornithine irreversible inhibits ornithine decarboxylase which is an important enzyme involved in hair growth.[5] Elfornithine does not remove hair through epilation or depilation but rather slows hair growths. Some side effects of eflornithine cream include acne, folliculitis, stinging or burning, skin irritation, redness, itching, and dizziness. Eflornithine cream is not meant to be used alone and is recommended to be combined with another hair removal technique.[26] The FDA only approved elfornithine cream for use on the face and other adjacent areas under the chin, and not the entire body.[31]

If the cause of hypertrichosis was due to a particular medication, the discontinuation of said medication usually reverses the effects of excessive hair growth.[2]