BY MARLEIGH SMITH, NEUROSCIENTIST AT DITTO
Ever wondered why birth control can influence hair growth? Why PCOS has you growing unwanted facial hair, but then it’s thinning on your scalp? Or why pregnancy gave you the best hair of your life - until 3 months postpartum when it all fell out? Your hormones are pulling the strings.
How Hair Grows
First, let's look at the basics. Hair growth occurs in three different stages:
1. Anagen - The Growth Phase.
Your hair strand is actively growing. This can last between 2-6 years. Don’t worry, most of your hair (85-90%) is in this phase at any given time!
2. Catagen - The Transition Phase.
Your hair strand is more stable. Hair growth stops in this phase, and the hair is no longer attached to the blood supply (but still attached to your head!). This is normally 1-3% of your hair at any given time.
3. Telogen - The Rest Phase.
RIP to your strand of hair. No hair growth is occurring, but the hair stays attached to your scalp until shedding occurs. This is normally 10-15% of your hair at any given time. Shedding usually occurs 3-6 months after this phase is completed.
Why this matters: hormones can impact which phase your hair is in! They can influence how your hair grows, how long it stays on your head, and even its quality.
How Hormones Affect Hair Growth
Estrogen: Your Hair’s Best Friend
Estrogen supports hair health in many ways:
-
Keeps Hair Growing Longer
When estrogen binds to receptors on your hair follicles, it triggers signaling pathways that activate growth genes, keeping your follicles in the growth phase (anagen) for longer.
- Creates an Anti-inflammatory Environment Around Follicles
Estrogen can also interact with immune cells which can promote an anti-inflammatory environment around the hair follicles. This supports a healthy environment for the hair follicle to grow!
- Converts Testosterone to More Hair-Healthy Estrogen!
It increases aromatase activity, which is an enzyme that turns androgens (e.g. testosterone) into estrogen. More estrogen = more hair growth!
Androgens (Testosterone) and Hair - It’s Complicated
The balance between estrogen and androgens matters for hair health. This can be an issue in conditions such as PCOS, where androgens may be elevated, or during menopause when estrogen drops and the relative amount of androgens increases.
Androgens (e.g.testosterone) affect hair differently depending on location. They stimulate hair growth on the face and body but can suppress it on the scalp.
Focusing on the scalp, androgens can inhibit growth signaling, leading to reduced hair growth. On top of this, testosterone can increase inflammatory cytokines and sometimes miniaturise hair follicles, creating an environment that's less supportive of healthy hair growth and maintenance.
What Happens When Hormones Go Awry and Impact Hair?
We’ll cover:
- PCOS
- Hormonal contraception
- Pregnancy & postpartum
- Menopause
1. Polycystic Ovary Syndrome (PCOS)
Women who have PCOS often have higher testosterone levels. This can result in certain challenges relating to hair:
Hirsutism: Higher testosterone levels promote the growth of hair in male sexual pattern areas such as the chin and chest. This is experienced by 70-80% of those with PCOS.
Female Pattern Hair Loss: In contrast, on the scalp, hair loss or thinning can occur, which happens in 22% of those with PCOS.
2. Hormonal Contraception
If you've taken hormonal birth control, you may have noticed your hair changed. Birth control can affect hair in different ways, though evidence is limited.
The first is hair loss after starting or stopping hormonal contraception (telogen effluvium). This may be because when synthetic hormones are suddenly introduced or withdrawn, the hormonal shift can trigger hair follicles to prematurely enter the resting (telogen) phase. Normal hair cycles keep about 10-15% of follicles resting at any time, but telogen effluvium can push that to 50%, causing noticeable shedding that typically begins 3-5 months after the change. The good news - it’s temporary, and it only affects a small proportion.
The second type is progressive androgenetic hair loss, which can develop in genetically predisposed individuals using contraceptives containing high-androgen progestins.
Finally, some contraceptives can actually improve hair, such as those containing anti-androgenic progestins.
3. Pregnancy & Postpartum
By mid-to-late pregnancy, many women have the thickest, most lustrous hair of their lives. This is because estrogen levels are high. Studies have found the percentage of hair in the anagen (growth) phase increases as pregnancy progresses, meaning less daily shedding than usual. Another study found that hair gets thicker, too!
Then comes the postpartum period, and your hair can feel like it’s falling out in clumps. This is because estrogen levels drop dramatically, and all those extra hairs that stayed in the growth phase during pregnancy now shift to the telogen phase, with immense shedding. It’s playing catch up, and don’t worry, it’s temporary!
4. Menopause
Hair changes during menopause are extremely common. Around 50% of postmenopausal women have female pattern hair loss (FPHL) - noticeable scalp thinning after menopause. This happens because estrogen levels drop dramatically, and the ratio of estrogen compared to available testosterone changes. Estrogen can no longer keep hair follicles in the anagen (growth) phase, and they start to switch to telogen (rest). In addition, more available testosterone in the bloodstream reaches hair follicles and inhibits hair growth on the scalp.
Estrogen is also an important factor of metabolism, which takes a hit as we enter menopause. Since hair follicles require energy to produce more hair, this can result in age related hair loss or a stunt in hair growth.
Finally, estrogen is a vasodilator (dilates blood vessels). Therefore, as we age and estrogen levels drop, there is less blood flow to hair follicles, which is dangerous for their health and growth.
Practical strategies to help
1. Nutrition
Nutrition is a powerful tool to help nourish your hair. Nutrients like omega-3 fatty acids can help create a healthy environment for hair growth. Additionally, vitamin D3 and zinc can help regulate hair cycles to promote hair growth. Iron supplementation can prevent hair loss and promote growth, as iron deficiency is an overlooked link to reduction or complete cessation of hair growth.
2. Managing stress
Studies have shown that stress induced hair loss is real - and it is bidirectional. The more you stress, the more hair you shed, and the more hair you shed the more stressed you can become.
Breaking this cycle requires stress management. Do what works for you - journaling, meditation, being in nature, breathwork and being with friends or family have all been proven to reduce stress.
3. Looking after your hair
Keeping consistent with your haircare helps to maintain shine, softness, and long-lasting hair health. Using a hair mask like the Miracle Mask from Josh Wood Colour helps to deeply condition, moisturise whilst restoring softness and strength. Pair this with gentle washing, heat protection, and regular trims to keep hair nourished, resilient, and looking beautifully healthy every day.
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