Psoriasis is a chronic inflammatory skin disease that affects approximately 3% of the world’s population. The most common form, known as psoriasis vulgaris, accounts for about 85–90% of all psoriasis cases. It is characterized by well-defined red plaques covered with silvery scales, commonly appearing on the elbows, knees, lower back, scalp, and umbilical region, although any part of the skin may be affected. The prevalence of psoriasis varies among countries depending on genetic, ethnic, and environmental factors. Moreover, psoriasis is associated with several other diseases, making it a systemic disorder rather than merely a skin condition. Several factors may trigger the onset of psoriasis or worsen its symptoms. One of the most important factors is bacterial infection and the imbalance of the skin microbiota. Infection with Streptococcus pyogenes has been linked to the development of guttate psoriasis, particularly in adolescents and young adults. Many patients experience sore throat symptoms or laboratory evidence of this bacterial infection before the appearance of psoriasis. It is believed that the bacteria stimulate the immune system through the production of superantigens, which excessively activate T-cells and provoke an inflammatory response in the skin. Another theory suggests that fragments from the bacterial cell wall are transported by immune cells from the tonsils to the skin, leading to inflammation. In addition, disturbances in the normal skin microbiota have been observed in psoriasis patients, with Staphylococcus aureus found more frequently in psoriatic lesions compared with healthy skin. Certain medications also play a significant role in triggering or exacerbating psoriasis. These drugs may induce psoriasis in genetically predisposed individuals or worsen existing disease in affected patients. Among the most notable medications is lithium, which is commonly used to treat psychiatric disorders. Lithium is thought to aggravate psoriasis by reducing intracellular cAMP levels and interfering with skin cell differentiation. Beta-blockers, which are widely prescribed for hypertension and heart diseases, have also been associated with increased psoriasis flare-ups in some patients. Psychological stress is another important factor involved in the development and exacerbation of psoriasis. Many patients believe that emotional stress and life pressures are closely related to their condition. Studies have shown that a considerable proportion of patients report stressful life events before the onset or worsening of psoriasis symptoms. Scientific reviews have also demonstrated that stress disorders may increase the likelihood of developing psoriasis, suggesting that psychological stress can contribute to triggering or intensifying the disease, although the exact relationship still requires further investigation. Hormonal and metabolic changes may also influence the course of psoriasis, especially in women. Symptoms often worsen during the menstrual cycle because of hormonal fluctuations, while many women experience significant improvement during pregnancy, and in some cases the symptoms may disappear completely. Research has indicated that higher estrogen levels relative to progesterone are associated with reduced disease severity, suggesting that estrogen may have a protective and beneficial effect on psoriasis. In conclusion, psoriasis is a complex disease influenced by multiple interacting factors, including infections, medications, psychological stress, and hormonal changes. Understanding these risk factors can help improve prevention strategies, disease management, and control of flare-ups, ultimately enhancing patients’ quality of life. Al Mustaqbal University The First University in Iraq