  For several decades optical tweezers have proven to be an invaluable tool in
the study and analysis of a myriad biological responses and applications.
However, as every tool, it can have undesirable or damaging effects upon the
very sample it is helping to study. In this review the main negative effects of
optical tweezers upon biostructures and living systems will be presented. Three
are the main areas on which the review will focus: linear optical excitation
within the tweezers, non-linear photonic effects, and thermal load upon the
sampled volume. Additional information is provided on negative mechanical
effects of optical traps on biological structures. Strategies to avoid or, in
the least, minimize these negative effects will be introduced. Finally, all
these effects, undesirable for the most, can have positive applications under
the right conditions. Some hints in this direction will also be discussed.
