Stress can cause hives in some people according to WebMD. Hives, also called urticaria, are red welts or spots that can appear on the skin due to stress or other causes. Although doctors do not know the exact reason for this reaction, it is believed that it may be connected to the immune system's response to stress.
Stress can produce chemical responses in the human body. This can heighten the skin's sensitivity and reactivity, leading to the possibility of rashes and hives. Likewise, stress can exacerbate certain skin conditions, such as psoriasis, rosacea, seborrheic dermatitis and acne.
When a person is experiencing stress, the body produces the hormone cortisol. According to the University of New Mexico, this hormone can change or suppress the body's immune system responses.
Besides stress, some other causes that can trigger hives are allergic reactions to certain foods, medicines, allergens and insect bites. Hives can cause itching and skin swelling. When hives cause a severe reaction, such as blocked airways, immediate medical attention may be necessary to avoid anaphylactic shock.