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Inaudible Sound Therapy and Hair Growth

A new study from South Korea that came out last month suggests a role for sound therapy in treating hair loss. It is titled “Induction of hair growth in hair follicle cells and organ cultures upon treatment with 30 kHz frequency inaudible sound.”

According to the authors, these inaudible frequency sound waves positively affect scalp hair via 4-hour treatments that:

Induce proliferative and anti‑apoptotic effects in human dermal papilla cells (hDPCs) and outer root sheath keratinocytes.

Inhibit the negative effects of dihydrotestosterone (DHT) upon hair growth.

The authors conclude that:

“Overall, the results suggested that inaudible sound may be effective in treating hair loss and could be used to develop a new hair loss treatment approach.”

They provide two hypotheses on why inaudible sound vibrations are causing hair growth:

The promotion of hair growth occurs due to activation of the Wnt/β-catenin signaling pathway via the sound waves.

The hair growth occurs as a result of mechanotransduction (mechanical stress) from the cell membrane of hair follicle cells. This stress is a result of modification by the inaudible sound.

Ultrasound Drug Delivery for Hair Growth

Note that ultrasound therapy and related devices are often used to improve drug delivery systems. In 2020, I discussed a study that used ultrasound activated nanoparticles to treat androgenetic alopecia. Also in the same year, I discussed sonophoresis and radio frequency as new potential ways to deliver topical finasteride.

A 2020 study from Taiwan found dual-frequency ultrasound to be effective for transdermal minoxidil delivery and hair growth enhancement. The authors found that ultrasound-mediated microbubble cavitation significantly increased both skin permeability and transdermal drug delivery.

Molecular Vibrations

This phenomenon is not as unbelievable as one would expect. For many years, we have known that even things like low-level laser light (LLLT) therapy, massage/mechanotherapy, scalp wounding, and even friction can lead to hair growth in some.

And in the way-out-there world, we have read anecdotal reports of hair regrowth on people who got unintentional scalp injuries from fire and even lightening. I think I should hereon call all such phenomena as “molecular scalp vibration” spurred hair growth.

The authors of this latest study cite a number of supporting studies. This includes ones that suggest that low-intensity vibrations and sound impact the body at the cellular and genetic level.

Years ago, when I first heard about wounding induced hair growth, I was not entirely surprised. We have read numerous examples of older men re-growing hair (after accidents and injuries) in areas of the scalp that had been bald for decades. My favorite example is of the below 78-year old man who accidentally fell into a fire, burnt his scalp, and got hair growth in return.

“Although interesting, it is difficult to see how this type of stimulation could be applied therapeutically”.

Scalp Burning Hair Regeneration — Hair growth after a burn injury.

Hair Growth After Cast Removal

My recent update on Follica made me think about the interesting phenomenon of hair growth after cast use. Many people who get arm or leg injuries have to use a plaster cast for several months. Upon removal of the cast, some people report a significant increase in the underlying body hair (i.e., hypertrichosis).

Today, I checked to see if there were any studies that discuss this unusual side effect from cast use. Lo and behold, I found some interesting ones with pretty extraordinary before and after photos. The below one is from a study from China titled: “Acquired Localized Hypertrichosis Induced by Internal Fixation and Plaster Cast Application”. The hands belong to a 15-year old boy who had to get a surgery and use a cast after a fracture.

The hair growth image in the actual study above is clearer, since I had to optimize the below image. The surprising thing is that this person has absolutely no hair at the back of the left hand. i.e., this is not just existing body hair becoming thicker. This is “new” hair growth after 6 weeks of cast use on the injured right hand. Kind of like Follica’s “de novo” hair creation concept. The new hair disappeared 4 months after the cast was removed.

Hair Growth After Cast Removal — Acquired localized hypertrichosis (ALH) after cast removal. Source: Annals of Dermatology.

Acquired Localized Hypertrichosis

It is not surprising that prolonged friction and enclosure from a plaster cast could make existing hair grow thicker. However, the creation of new hair is very unexpected. Yet another example below from Hong Kong shows hair growth on the right leg of a 28-month old child. That leg had been in a cast for 6 weeks after a fracture. Note that lack of any body hair on the left leg.

Per the authors of the first study that I discussed above, the acquired localized hypertrichosis (ALH) results from: “chronic irritation, inflammation, friction, and occlusion” by the plaster of Paris cast.

And yet another example from Hong Kong is even more striking. This time on the left forearm (of a 16-year old boy) that had been in a splint. Note again that there is no body hair at all on the right forearm. i.e., this person does not normally have hair on any arm.

Hair Growth after Splint. Source: Case Reports in Pediatrics.

If I only found examples of thicker hair growth, I would not have written this post. However, all three examples that I presented above show brand new localized hair growth.

Although this post is not exactly related to wounding, I can’t help but think of the following quote from Follica:

“Following skin disruption, cells that migrate to help healing are forced to make a decision: Should I make epidermis, or should I make a hair?“

Of course none of us would ever be indecisive given such a choice.