The effects of stress - physical or mental stresses may cause physical illness as well as mental or emotional problems. Here are parts of the body most affected by stress. Hair - high stress levels may cause excessive hair loss some forms of baldness. Brain - stress triggers mental emotional problems such as insomnia, headaches, personality changes, irritability, anxiety depression. Muscles - spasmodic pains in the neck shoulders, musculoskeletal aches, lower back pain.