What You Notice
For many women, hair change is one of the most upsetting parts of this transition, precisely because hair is so tied to how we feel about ourselves. It usually creeps up quietly. You tie your hair back and the band goes round an extra time because the ponytail is thinner in your hand. You notice your parting looks a little wider than it used to, and in bright light or in photographs more scalp shows through than you remember. The hairline around your temples may soften.
You start finding more hair everywhere, on the pillow in the morning, gathered in the shower drain, on your clothes and wound around your brush, and it can be genuinely frightening to see how much is coming out. Your hair may also feel different in itself, finer and flatter, without the body and volume it once had, so styles fall flat and blow drying does not give the lift it used to. One important detail is the pattern. This kind of hormonal thinning is usually diffuse, meaning it is spread fairly evenly across the top and crown of your head, rather than showing up as distinct round bald patches or sudden clumps in one spot. That different pattern points to other causes and is worth showing a doctor rather than waiting.
Why It Happens
Your hair grows in a cycle. Each strand spends a long stretch actively growing, then a short resting phase, then it sheds to make room for new growth, and normally only a small share of your hair is resting or shedding at any time. Estrogen and progesterone help keep hairs in that active growing phase for longer, so while your hormones were steady, your hair stayed fuller. As these hormones fall in perimenopause, more hairs slip into the resting and shedding phase at the same time, so you shed more, and each new hair can grow back a little finer and weaker than the one before.
At the same time, as estrogen drops, the relative influence of androgens, the group of hormones that includes testosterone, becomes greater, and in women who are genetically prone to it, this drives what is called female pattern hair loss, a gradual shrinking and thinning of hair across the top of the scalp. Here is the part that really matters though. Hormones are far from the only cause of thinning hair in your 40s, and often they are not even the main one. Low iron stores, which are extremely common in women, an underactive or overactive thyroid, low vitamin D, a recent illness or surgery, high stress, and crash dieting or rapid weight loss can all trigger significant shedding, and it often shows up a few months after the trigger, which makes it hard to connect the dots. Because so many of these causes are common and genuinely fixable, getting tested is the sensible first step rather than assuming menopause is entirely to blame and doing nothing.
Educational only, not medical advice. Further reading: American Academy of Dermatology (aad.org), reviews on female pattern hair loss and shedding, a study comparing rosemary oil and minoxidil, NICE guideline NG23.