Stress encompasses a range of physical and physiological responses to a specific situation. It can induce mental, emotional, or physical symptoms. It can have an impact at the cellular level and on hair follicles, leading to hair loss. Let's explore how stress operates in this article.
Reactive Hair Loss: What is the connection between hair loss and stress?
Why do we lose hair?
Hair loss is a daily phenomenon but is entirely normal. Indeed, each hair has its own life cycle composed of three phases:
The Anagen Phase (2 - 6 years): This is the growth phase of the hair during which there is proliferation of the matrix cells that form the inner sheath of the root, the cortex, and the medulla of the hair shaft. The synthesis and pigmentation of the hair shaft only occur during this phase. Its duration determines the length of the hair, generally 1 cm per month.
The catagen phase (2 - 3 weeks): The first sign of the catagen phase is the cessation of melanin production, the pigment responsible for the color of our hair, in the hair bulb. The hair stops growing but remains attached to its hair follicle.
The telogen phase (2 - 3 months): After the catagen phase, the follicles rest in a dormant stage, the telogen phase. The hair shaft eventually detaches from its follicle, which is already beginning to produce a new hair beneath the skin.
Thus, within a head of hair, not all hairs are necessarily in the same phase as they each have their own independent life cycle. Some may be in a growth phase, while others are about to shed. This is why we naturally lose between 50 and 150 hairs per day. Their life cycles are regulated by hormonal or nutritional variations.
How does stress impact hair loss?
During periods of stress, many people have noticed that their hair loss is more significant than usual. Therefore, researchers have delved into the subject to try and understand the biological or molecular links that could explain this observation.
Studies on mice have provided the first evidence that stress plays a role in hair loss. Indeed, stress can lead to the release of substance P by the sensory nerve fibers in the skin. This locally released substance P can directly inhibit the growth of keratinocytes in hair follicles or induce their apoptosis and inhibit their proliferation through the release of hair growth inhibitory cytokines such as TNF-α and IL-154, 55 from macrophages and mast cells. The TNF-α is a mediator of inflammation that serves to transition the hair into the telogen phase, which is their shedding phase. Moreover, previous studies had already demonstrated that an intracutaneous injection of substance P could inhibit hair growth and induce premature regression of the hair follicle through apoptosis. Therefore, it can be concluded that stress disrupts the hair life cycle by hastening the transition to the catagen phase and then to the telogen phase promoting hair loss.
For your information: this substance P binds to the neurokinin 1 (NK1) receptors. The results of this study have therefore led to research to find NK1 antagonists that can counteract the negative effects of stress on the hair follicle.
ARCK P. C. & al. Indications for a brain-hair follicle axis: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P. The FASEB Journal (2001).
HADSHIEW I. M. & al. Burden of Hair Loss: Stress and the Underestimated Psychosocial Impact of Telogen Effluvium and Androgenetic Alopecia. Journal of Investigative Dermatology (2004).