Skin pigmentation
Melanin is a pigment in the epidermis that functions to protect keratinocytes from the damage caused by UV radiation; it is found in higher concentrations in the epidermis of darker-skinned individuals, affording them protection against the development of AKs. Fair-skinned individuals have a significantly increased risk of developing AKs when compared to olive-skinned individuals (odds ratios of 14.1 and 6.5, respectively), and AKs are uncommon in dark-skinned people of African descent. Other phenotypic features seen in fair-skinned individuals that are associated with an increased propensity to develop AKs include:
Freckling
Light hair and eye color
Propensity to sunburn
Inability to tan

Other risk factors
Immunosuppression: People with a compromised immune system from medical conditions (such as AIDS) or immunosuppressive therapy (such as chronic immunosuppression after organ transplantation, or chemotherapy for cancer) are at increased risk for developing AKs. They may develop AK at an earlier age or have an increased number of AK lesions compared to immunocompetent people. Human papillomavirus (HPV): The role of HPV in the development of AK remains unclear, but evidence suggests that infection with the betapapillomavirus type of HPV may be associated with an increased likelihood of AK. Genodermatoses: Certain genetic disorders interfere with DNA repair after sun exposure, thereby putting these individuals at higher risk for the development of AKs. Examples of such genetic disorders include xeroderma pigmentosum and Bloom syndrome. Balding: AKs are commonly found on the scalps of balding men.
Hypothenar hammer syndrome (HHS) is a vascular occlusion in humans in the region of the ulna. It is caused by repetitive trauma to the hand or wrist (such as that caused by the use of a hammer) by the vulnerable portion of the ulnar artery as it passes over the hamate bone, which may result in thrombosis, irregularity or aneurysm formation. HHS is a potentially curable cause of Raynauds syndrome, distinct from hand–arm vibration syndrome. Cause
Diagnosis
A physical examination of the hand may show discoloration (blanching, mottling, and/ or cyanosis; gangrene  may be present in advanced cases), unusual tenderness/ a callous over the hypothenar eminence, and fingertip ulcerations and splinter hemorrhages over ulnar digits; if an aneurysm is present, there may also be a pulsatile mass. Allens test will be positive if an occlusion is present and negative if an aneurysm is present. An angiogram may show a "corkscrew" ulnar artery or an occlusion or aneurysm at the hook of the hamate. Treatment
Noninvasive treatments have an 80% success rate; Example: switch jobs, stop smoking, regular finger exercise, surgical options exist for other instances. Epidemiology
HHS, though rare, occurs much more frequently in men than in women (9:1) and principally affects those in their 40s and 50s. == References ==