A Cyclobutane Pyrimidine Dimer (CPD) is formed by the linkage of two adjacent pyrimidines.

CPD’s have many effects on the human body such as erythema (sunburn), suppression of the immune system, and more seriously, mutation and skin cancer, which can lead to death (16). They are most frequently found in the p53 gene, also known as the tumour suppressor gene, and
involve either C to T, CC or TT mutations (17).
To avoid and reduce the risk of these effects it is important to repair these damaged cells, see Repair Processes.