The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific and philosophical concepts

Why do eyebrows and eyelashes stop growing at a certain point, yet it seems other hairs would grow and grow if you let them? Thomas Carnegy, Angus

Send new questions to nq@theguardian.com.

Anything else would be hair-raising. Anthony Walter

Because, back in the day, the mat caused by the eyebrow and eyelash hair eventually tangling together either kept the eyes held open all night – which led to exhaustion and an inability to run fast, which led to being eaten by saber-toothed tiger – or made it impossible to see at all – which led to being eaten by saber-toothed tiger cubs looking for an easy meal. Thus those people were swiftly removed from the genetic tree. Evolution at work! Thomas1178

Hairs have an active growing period and then a transition phase before reaching the falling-out phase. Seeing as we never have to trim our eyebrows, I guess their growth period is short. DianaB

We never have to trim our eyebrows? Speak for yourself: those of us aged about 56 or so need to have this done to stop looking like Denis Healey. (Ask your grandfather.) PhilipPigott

I inherited a number of traits from my father, including Healey-esque eyebrows, which I’ve needed to trim regularly since at least my 30s. I’m a woman. EBGB

They don’t stop growing, if you are a woman, they just migrate to other areas. Chin, upper lip, nipples. DoraMarr

If you’re a man it, hair can migrate from the top of the head to everywhere else. IndebtedYouth

As men of a certain age will testify, eyebrow hairs can certainly just grow and grow, along with nose hair, ear hair etc. As for eyelashes, they fall out over time and then regrow. There is an optimal length beyond which they are more likely to fall out, especially when eyes are rubbed. Peter, Bristol

More interesting is why my ear hairs started growing and now need cutting every time I get a haircut. What possible evolutionary advantage can accrue from that? Sandancer56

When I was younger, I had lovely long, curly eyelashes, which I passed on to both my sons and my grandson. (No female descendants to benefit.) Now, my eyelashes seemed to have stopped growing and are short. I am over 70, so is it old age? LucyAnnie

The only body hair that doesn’t stop growing is the stuff on your head, and beards I suppose. Everything else grows to a certain length and then drops out/is replaced, which is just as well. It wouldn’t be very convenient if leg/body/pubic/underarm/eyelash/eyebrow hair grew continuously.

I don’t know why human head hair grows so long – there aren’t any other animals in which this happens. Can someone answer that one? Dunnock_Mk2

When I got pregnant, I had awful afternoon sickness. From about 4pm every day, my head was down the toilet. I was terrified of taking any drug or remedy in case my much longed-for pregnancy was lost. Month three, the good nails kicked in and to my astonishment my eyelashes started growing freakishly long. Each hair was a different length. One grew to just under 5in (13cm). It was all curled up at the edge. I started thinking about contacting Guinness World Records. As they fell out, I kept them in a plastic drawer thing I kept odds in. Wonder where that went. WishfulStinker

Unlike all the gentlemen who have wildly luxurious eyebrows (my husband included), mine have almost disappeared, along with my eyelashes. I never plucked and used to have a nice, well-defined brow. Now, in my 60s, they are sparse and showing a preference to curling up like Fu Manchu. I have also lost almost all hair on my arms and legs (except for my knees – why?). Getting older is weird in many ways. Chooks59

I’m afraid I don’t know the answer, but I’d just like to say that, at a time when the Guardian is often lazily accused below the line of dumbing down, it’s a great comfort to know that you can always rely on Notes and queries to sturdily refute that contention by maintaining an elevated intellectual tone and daring to confront the most recherché, recondite and even controversial of topics. A case in point is this week’s query – which demonstrates yet again that no question is too eyebrow to raise. ThereIsNoOwl