Blackheads are a mild form of acne that appear as unsightly, open pores that appear darker than the skin surrounding them. They get their dark appearance from a skin pigment called melanin, which oxidizes and turns black when it's exposed to the air. Blackheads aren't caused by dirt, but by sebum (oil) and dead skin cells blocking the pore. If the pore remains open, it becomes a blackhead; if it's completely blocked and closed, it turns into a whitehead.
Therefore, it is very important that you wear sunscreen everyday, with an SPF of 30.Of note, after SPF 30, there are decreasing marginal returns in UVB protection. The % of UVB protection as a function of SPF Value is a log graph and plateaus after SPF 30. Therefore, there is not much difference in protection between SPF 40 and 50. Sunscreens with an SPF 100 are banned in some countries.
Drugs: Some medications may cause or worsen acne, such as those containing iodides, bromides, or oral or injected steroids (either the medically prescribed prednisone [Deltasone, Orasone, Prednicen-M, Liquid Pred] or the steroids that bodybuilders or athletes sometimes take). Other drugs that can cause or aggravate acne are anticonvulsant medications and lithium (Eskalith, Lithobid). Most cases of acne, however, are not drug related.