This study aims to perform an internally validated genome-wide association study of actinic keratoses (AKs) in a group of patients in the Research Program on Genes, Environment and Health (RPGEH) known as the Genetic Epidemiology Research on Aging cohort. Investigators will conduct single nucleotide polymorphism (SNP)-specific stratified Cox-type regression of time to post-enrollment AK in two randomly partitioned subgroups of the cohort, adjusting for gender, age at RPGEH enrollment and principal components of ancestry. SNP regression coefficients in the two subgroups will be optimally combined to select AK-associated SNPs whose combined coefficients meet genome-wide statistical significance. AK-SNPs will also be compared with squamous-cell-carcinoma-SNPs. Additionally, the role of sex in AK risk will be examined by investigating mitochondrial genetic variation and by testing individual mitochondrial SNPs for association with AK in men and women separately. Finally, individual subjects’ mitochondrial haplogroups will be determined and tested for association with AK.