There were 1302 listings for acrylic nails on Ebay when I wrote this, more than half of them could harm you.
Acrylic nails are false nails that are pasted on to the real nail, they're made from a combination of powder and liquid. A lot of the nails sold here are made from methyl methacrylate or MMA as it is referred to in many auctions.
Methyl methacrylate can cause you to develop serious skin conditions and it can lead to deformities in natural growth. The only reason MMA is used by manufacturers of acrylic nails is because it is cheaper to produce than ethyl methacrylate (EMA).
EMA nails cost more to manufacture so usually they're more expensive to buy, even on Ebay, but that extra expense removes the risk of unwanted side effects turning a fun purchase into a nightmare.
If the auction you're looking at doesn't specify whether the nails contain MMA or EMA then ask the seller before you bid or buy them.
Well fixed acrylics look great and can make you feel more confident, especially if you can't get your real nails to grow evenly so don't let this put you off using them.
They can also be great fun if used properly but please buy with care !!