1- Hormones: It is now well established that androgenic hormones leading to pore blockage and raised oil formation in acne. Pore blockage leads to buildup of oil within the pore (blackheads and whiteheads). As the oil becomes blocked in the pore, bacteria start to grow, leading to inflamed red bumps or "zits" (papules, pustules). many of these large sacs of oil may rupture, causing large red lumps (nodules). Dermology
2- Scrubbing: If you scrub with an abrasive soap or pick at your skin or rub it too much, the walls of the pores can break and cause more pimples. Squeezing or popping blackheads and whiteheads usually causes added problems, including scars. Too much washing (more than 2 or 3 times a day) can make your skin dry and cause the oil glands to work harder.
3- Certain foods: Foods like chocolate, sweets, colas, and fried foods do not make acne worse. however if a certain food does seem to make acne worse, try eliminating it for a few weeks and see if that helps. New studies suggest that milk products could aggravate acne in some patients.
4- Certain make up / hair care products: Some types of makeup could block pores; a water-based, oil-free makeup is preferred. Moisturizers containing oil could additionally make acne worse. Avoid oil-based moisturizers and cocoa butter. Also, do not use any greasy makeup removers. Similarly, hair length and grooming products such as conditioners, gels and hairspray may contribute to acne by blocking pores. Damp hair could also contribute to acne if allowed to come into contact with the neck, back, and shoulders for long periods of times.
5- Psychological / mental stress: Psychological factors (stress, negative emotions) can affect the generation and aggravation of skin disorders, that could result in some skin diseases especially acne. In addition, environmental toxicity can also worsen acne.
Considering the aggravating role of the above mentioned factors in acne, acne prevention can be achieved by avoiding these aggravating factors which can block pores, especially some thick moisturizer creams, retained sweat or moisture under hats, pads, helmets and damp clothing.