• Intact skin (epidermis and dermis)

mechanical barrier impermeable to most infectious agents.

lactic acid and fatty acids present in sweat and sebaceous secretions inhibit microbial growth due to acidic pH.

• Mucus membranes

secrete mucus which traps foreign particles such as bacteria

prevents them from adhering to epithelial cells

Normal bacterial flora inhibit the growth of many potentially pathogenic bacteria

Physiologic Barriers

body temperature and the fever

response inhibit the growth of certain microbes

acid pH of the stomach

kills most microorganisms

various contain substances with anti-bacterial activity; gastric juice - acid; tears, saliva, nasal secretions - lysozyme milk - lactoperoxidase; semen - spermine and zinc;