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.
The Imiquimod 3.75% cream has been validated in a treatment regimen consisting of daily application to entire face and scalp for two 2-week treatment cycles, with a complete clearance rate of 36%.While the clearance rate observed with the Imiquimod 3.75% cream was lower than that observed with the 5% cream (36 and 50 percent, respectively), there are lower reported rates of adverse reactions with the 3.75% cream: 19% of individuals using Imiquimod 3.75% cream reported adverse reactions including local erythema, scabbing, and flaking at the application site, while nearly a third of individuals using the 5% cream reported the same types of reactions with Imiquimod treatment. However, it is ultimately difficult to compare the efficacy of the different strength creams directly, as current study data varies in methodology (e.g. duration and frequency of treatment, and amount of skin surface area covered). Ingenol mebutate gel
Ingenol mebutate is a newer treatment for AK used in Europe and the United States. It works in two ways, first by disrupting cell membranes and mitochondria resulting cell death, and then by inducing antibody-dependent cellular cytotoxicity to eliminate remaining tumor cells. A 3-day treatment course with the 0.015% gel is recommended for the scalp and face, while a 2-day treatment course with the 0.05% gel is recommended for the trunk and extremities. Treatment with the 0.015% gel was found to completely clear 57% of AK, while the 0.05% gel had a 34% clearance rate. Advantages of ingenol mebutate treatment include the short duration of therapy and a low recurrence rate.