Nov 12, · The sun's ultraviolet rays can increase inflammation and redness, and can cause post-inflammatory hyperpigmentation (dark discoloration). Some acne medications may make your skin more sensitive to. Sun sensitivity, sometimes called photosensitivity, is defined by the Genetics Home Reference, part of the U.S. National Library of Medicine, as an "abnormal reaction to sunlight." Acne rashes, skin bumps and pimples may be a result of skin sensitivity 3. Assessment by a dermatologist is necessary to determine the exact cause.