Too Much Stress. The way stress affects the immune system is complicated but explained well by Harrison Wein, Ph. D, in the National Institutes of Health newsletter, Word on Health.. In the article, Stress and Disease: New Perspectives, Dr. Wein states that stress produces a hormone in the body called cortisol. report in the November 1990 edition of Psychological Bulletin, states that stress suppresses immune system function and that, over time, the immune system does not adapt but instead continues to wear away. What was intended to protect the body, begins to harm it when unregulated.