Xeroderma pigmentosa (XP) is a rare autosomal recessive disorder caused by mutations in one of the nucleotide excision repair (NER) genes (XPA–XPG) or in the POLH gene (XP variant type). These genes normally repair DNA damage caused by ultraviolet (UV) radiation. When this repair pathway fails, UV-induced DNA damage accumulates in skin cells rather than being corrected, leading to severe photosensitivity, early freckling, premature skin aging, and a dramatically elevated risk of skin cancers from a very young age. In about a third of patients, progressive neurodegeneration also occurs due to unrepaired DNA damage in neurons.

In simple words, It happens when the body’s natural “DNA repair system” doesn’t work properly. Normally, when sunlight (UV rays) damages our skin cells, our body fixes that damage automatically. In XP, this repair process doesn’t happen the way it should — so damage builds up over time.

This is why people with XP get severe sunburns very easily, develop freckling and skin changes at a young age, and have a much higher chance of developing skin cancer early in life. In some cases, it can also affect the nervous system over time.