The benefits of caffeine on hair growth.

Hair loss is a widespread issue affecting many men and women globally. Over 80% of men and more than 30% of women report suffering from hair loss for one reason or another. Others are concerned about their thin or sparse hair. It is therefore not surprising that scientists have sought solutions to stimulate hair growth and thus give existing hair a thick and "plumped" appearance. One of the leading ingredients is caffeine . Indeed, according to available research, it appears to have a stimulating effect on the growth of hair follicles to improve hair density and strength by acting on various parameters. Here's what has been discovered.

• Caffeine enhances the ability of hair to grow and extends its growth phase (anagen phase). A 2017 study revealed that when caffeine was topically applied to human hair follicles ex vivo at concentrations of 0.001% and 0.005%, researchers observed an extension of the anagen phase and an elongation of the hair shaft, resulting in longer and thicker hair roots. They demonstrated that caffeine can counteract the suppressive effects of dihydrotestosterone (DHT) in the hair follicles of both men and women on hair growth.

  Indeed, when this androgen is present in excess, it induces a gradual shortening of successive anagen phases in favour of longer resting phases (telogen phase), followed by a gradual "miniaturisation" of genetically predetermined hair follicles. These follicles, after several growth cycles, eventually cease to grow, leading to androgenetic alopecia. Caffeine acts by inhibiting the activity of 5-alpha reductase, an intrafollicular enzyme that converts testosterone into DHT.

  The transition between the different phases of the hair follicle cycle is a process controlled and regulated by growth factors. However, in another study, it was shown that caffeine also allowed for a higher expression of IGF-1, a promoter of hair growth in both male and female hair follicles, and a lower expression of TGF-β2, a significant regulatory factor that opposes hair growth in male follicles and promotes the catagen phase (regression phase). These conditions are favourable for maintaining the anagen phase. Therefore, caffeine could potentially prevent hair loss and encourage hair growth.

• Caffeine stimulates the proliferation of keratinocytes in the hair matrix. In a study, it was demonstrated that caffeine could increase keratinocyte proliferation in the dermal papilla. However, higher concentrations of caffeine (100, 500 and 1,500 μg/mL) had inhibitory effects, potentially causing over-stimulation of hair follicle metabolism, significant consumption of energy reserves, and exhaustion of the proliferation capacity.

  These growth-stimulating effects can be explained by its ability to inhibit the activity of phosphodiesterase, an enzyme responsible for the degradation of cAMP into 5-AMP. This then leads to an increase in cAMP levels within the cells, thereby promoting their proliferation by stimulating cellular metabolism. This mechanism can counteract the miniaturisation of the hair follicle induced by DHT.

• Caffeine facilitates the delivery of oxygen and nutrients to hair follicles. Caffeine is known for its vasodilatory properties, meaning it has the ability to improve the microcirculation of blood vessels in the scalp, thereby increasing hair density. This effect can be enhanced by an active scalp massage to allow it to penetrate the skin and act during the application of the hair product. However, the concentration of caffeine must be sufficiently low to increase flow and not cause the opposite effect, that is vasoconstriction, or a limitation of blood flow.

Note : Female hair follicles appear to be more sensitive to caffeine than male hair follicles,

Thus, it has been proven that caffeine has stimulating effects on hair growth. It therefore appears to be a promising candidate in the prevention of hair loss and the management of alopecia. It can either exert a complementary effect by targeting other mechanisms, or act in synergy with established anti-androgenic drugs. Beyond alopecia, caffeine can also be used as part of a beneficial hair care routine for ageing hair, to combat thinning and hormonal hair loss, for example.

Moreover, unlike the topical solution of 2 or 5% minoxidil (for men and women) or orally administered finasteride (for men only), two drugs approved for the treatment of alopecia, the use of hair products containing caffeine does not present any obvious side effects or contraindications. As always, it is advisable to carry out a patch test before using any new product in order to reduce the occurrence of potential irritation risks.

However, it is crucial to clarify that additional research is required to confirm and establish the role of caffeine in hair growth, and that there is no "miracle molecule" capable of independently promoting hair growth.

To reap the benefits of caffeine for hair, thetopical application on the scalp is the quickest and most suitable method of administration, through a shampoo, conditioner, or serum. A number of studies have even shown that caffeine can penetrate both the skin of the scalp and reach the hair follicle. However, for the caffeine to penetrate to the root of the hair and produce an effect, rub your scalp or leave the hair product on for a minimum of 2 minutes. It can remain there for up to 48 hours even after washing the hair.

Note : The quantity of caffeine to be consumed orally (equivalent to 50 to 60 cups of coffee) to achieve noticeable results in hair growth is higher than the recommended amount, set at around 400 milligrams per day (about four or five cups of coffee) by the FDA. This limit is generally not associated with dangerous and negative health effects (risk of myocardial infarction, epileptic seizure, dependency, anxiety, headaches, etc).