The formation of acne is, in most cases, connected with hormonal changes, as is common in puberty. Another cause may be hormonal imbalances during one's period, after discontinuing the use of contraceptives or during pregnancy.        

In addition, medication, stress and a genetically predisposed sensitivity to irritants (comedogenic substances) causing blackheads can play a role in the formation of acne. Comedogenic cosmetics are primary external triggers. That's why it is recommended that you check your toiletry bag. The ingredient declarations on the packages will tell you which products to ban from your toiletry bag. All products should have a "non-comedogenic" claim on them.