What are those white marks/lines on fingernails caused by??

[neverlookback]

I've had the occasional one and they seem to grow out or disappear, my 20m dd seems to have them across most of her nails half way up, I've noticed them today, she does trap her fingers a lot so could it be damage under the nail?
I'm sure I was told it can mean your not getting enough calcium but I think she does, she was lactose intol as a baby but weaned onto dairy at 12m and has tons of milk cheese etc
I'm sure it's nothing but just want to know what causes them??
Thanks

If they go across the nail, they are usually caused by damage to the nail bed - ie just below the bottom of the nail, so they will appear a bit after the damage, as the nail grows out. If she has them across a number of nails in a similar place at the moment, she probably bashed the whole lot in one go!

White marks running up and down the nail are meant to be a sign of calcium deficiency I think. Plus also age can make a change - mine are very ridged that direction (40s) and they weren't when I was younger.

HTH