Numerous factors may reduce an individual's defenses against pathogens. Several injuries including abrasions (scratches), lacerations (tears), contusions (bruises), incisions, punctures, and fractures (bone breaks) decrease the body's defenses against microbes. The loss of vital signs, such as a drop in blood pressure, prevents sufficient blood from reaching tissues and maintaining good health. Two types of shock (drop in blood pressure) are primary or cardiogenic caused by trauma and dilation of blood vessels and secondary or hypovolemic shock caused by loss of blood. Emergency medical treatment personell must evaluate and recognize the causes and types of shock.

Other factors that reduce the ability to defend against pathogens include blocked circulation and exteme change in tissue temperature. An attached clot (thrombus) or moving clot (embolism) may prevent a body organ from functioning properly and assisting in the body's defense against microbes and toxins. Also extreme chilling of tissues (hypothermia) and elevation of tissue temperature (hyperthermia) damage cells and reduce cell activity. Frostbite and burns inhibit the skin from protecing the body against pathogens. Severe third degree burns also limit the normal regeneration process.

Many chemicals used to assist in maintenance of health can become damaging if abused. Antibiotics known to inhibit pathogenic bacterial growth will also inhibit normal beneficial microbes. Aspirin which thins blood and relieves pain may upset electrolytes if over used. Cortisone reduces swelling and relieves itching from poison ivy, but abusive use of cortosones may suppress lymphocytes and the ability to defend against microbes. Oral contraceptive may help in family planning by eliminating conceptions, but long term use has been related to increased blood clots. Alcohol thins blood and helps remove stress, but alcohol abuse damages liver and reduces responses to dangers. Anesthetics relieve pain but may also cause allergic reactions. Tranquilizers help individuals relax, but over use has been related to abnormal bile salt formation. Many of these chemicals have the potential to reduce human defenses against micro-organisms.

Finally, the exposure to pathogens certainly has the possibility of reducing the body's defense against microbes. Pathogens sometimes produce and release poisons (toxins). Endotoxins and exotoxins; as well as neurotoxins, hemotoxins, myotoxins, and enterotoxins interfere with normal health. In addition, some pathogens have enzymes like coagulase and hyaluronidase which tend to increase the survival and spread of pathogens in the host.