In PCR, primer dimers are undesirable byproducts that can interfere with the amplification of the target DNA. They form when primers, short pieces of DNA that bind to the ends of the target DNA, anneal to each other instead of to the target DNA. This can lead to the formation of primer-dimer products, which are shorter than the target DNA and can compete with the target DNA for binding to the primers. As a result, primer dimers can reduce the efficiency of PCR and lead to false positives.
There are several ways to avoid primer dimers. One way is to use a higher annealing temperature. This makes it less likely that the primers will anneal to each other, as the higher temperature will favor the formation of primer-target complexes. Another way to avoid primer dimers is to use a shorter annealing time. This reduces the amount of time that the primers have to anneal to each other, which also reduces the likelihood of primer-dimer formation. Finally, using a higher concentration of primers can help to reduce primer dimers, as this will increase the likelihood that the primers will anneal to the target DNA rather than to each other.