Common causes of acne include:

1. Excess oil production: Overactive sebaceous glands produce too much oil.

2. Clogged hair follicles: Dead skin cells and oil block pores.

3. Bacteria: Propionibacterium acnes bacteria can trigger inflammation.

4. Hormonal changes: Fluctuations during puberty, menstruation, pregnancy, and stress.

5. Diet: High glycemic index foods and dairy products may exacerbate acne.

6. Medications: Certain drugs, like corticosteroids, androgens, and lithium.

7. Genetics: Family history of acne can increase the risk.

8. Cosmetic products: Comedogenic products can block pores.

9. Environmental factors: Pollution and humidity can worsen acne.

10. Stress: Can exacerbate acne by causing hormonal changes.