Formication is the sensation of insects crawling on or under the skin when nothing is there. It's a real neurological symptom, not imagination, and in women it's most commonly perimenopausal — driven by the effects of falling estrogen on peripheral nerve function and histamine metabolism.
The physiological basis:
- Estrogen supports peripheral nerve myelination and neurotransmission. As estradiol declines through perimenopause, peripheral sensory nerves become more excitable and more prone to producing spontaneous sensations.
- Estrogen affects histamine metabolism. As estrogen falls, histamine sensitivity often rises. This can produce a range of skin sensations including itch, crawling, tingling.
- Sleep disruption amplifies the sensation. Formication is often reported at night or during periods of high stress — cortisol and poor sleep both worsen it.
Other conditions can produce formication too — vitamin B12 deficiency, certain medications, thyroid dysfunction, alcohol/substance withdrawal, chronic stress. If it's persistent and not clearly cyclical, worth ruling those out.
What helps in the perimenopausal case: consistent sleep, stress management, adequate B12, and — where appropriate — HRT (which has been reported to reduce formication in multiple clinical reports, though there aren't large randomized trials specifically for this symptom).
Blood markers worth checking: estradiol, B12, ferritin, hs-CRP.