This article is from the Piercing FAQ, by Anne Greenblatt with numerous contributions by others.
Acrylic
Acrylic jewelry is most often worn in enlarged piercings when
light-weight jewelry is desired. Acrylic is not intended to be worn in
fresh or unhealed piercings. There is some debate among piercers
regarding the safety of long term wear. Acrylic has not been
clinically proven to be safe for wear in the body. Jewelry should be
inspected frequently for scratches which can irritate the piercing and
trap bacteria.
Acrylic is very brittle and will shatter under stress. For releasing
beads in captive bead rings, first warm the ring in the palm of your
hand; do not use ring-expanding pliers. Acrylic cannot be
autoclaved. Extended exposure to any type of alcohol will degrade
acrylic jewelry.
Nylon / Teflon
Monofilament nylon and teflon are used where a more flexible piece of
jewelry is desired or if the wearer is senstive to metals. Both can be
autoclaved.
Securing monofilament is often difficult. Appropriately bored threaded
metal balls can be screwed onto the ends; the metal threads will cut
threads in the monofilament. The ends may be flattened into a disc
shape using a hot knife but the results may not be smooth or
comfortable.
 
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