I take good care of my hair but my edges are visibly thinning since I started wearing an undercap every day. It is scaring me. Has anyone actually fixed this, or is it just part of covering?
It is almost always tension, not the covering itself. Three things fixed my edges: stop tying the cap tight (snug, not gripping), never tie wet hair up under it, and switch to a soft seamless or velvet-band undercap instead of the thin scratchy ones. The band spreads the pressure instead of digging into one line. The best undercaps compared post breaks down which ones are gentlest.
Change where your bun or tie sits every few days so the same spot is not pulled constantly. Mine recovered once I stopped parting and tying in the exact same place daily.
Rosemary oil and a gentle scalp massage a few times a week genuinely brought my hairline back over a couple of months. Be patient with it.
Please get a quick blood test too (iron, vitamin D, thyroid). Loads of us blame the hijab when it is actually a deficiency. There is a full write-up here: hijab and hair loss.
Silk or bamboo undercaps over cotton for me, way less friction on the baby hairs. Also see healthy hair under hijab.