I've heard of people getting infections under acrylic nails, but have never experienced such a problem myself.

The nails do suffer to some extent from not breathing when they are covered by acrylic. They get thinner and weaker over time. This causes some people to take a break on the acrylic nails for awhile and let the natural nails grow out fully with no covering to restore themselves.

You have to watch what's happening with your own nails and judge accordingly if it's time to stop on the acrylic nails for awhile.

What I do to help the nails breathe is I let them grow out for at least 6 weeks before filling in with acrylic fills at the back. This means that almost half the length of the nail is exposed to the air before I get it covered over with acrylic. I figure that helps maintain nail strenght and health.