Infections cause considerable morbidity and mortality in patients with diabetes mellitus. Infections may precipitate metabolic derangements, and conversely, the metabolic derangements of diabetes may facilitate infection. Hyperglycemia and acidemia exacerbate impairments in humoral immunity and polymorphonuclear leukocyte and lymphocyte functions but are substantially reversed when pH and blood glucose levels return to normal.[5] Although the exact level above which leukocyte function is impaired is not defined, in vitro evidence suggests a blood concentration of 200 mg/dL as a possible threshold.[6] Patients with long-standing diabetes tend to have microvascular and macrovascular disease with resultant poor tissue perfusion and increased risk of infection. Moreover, the ability of the skin to act as a barrier to infection may be compromised when the diminished sensation of diabetic neuropathy results in unnoticed injury. Diabetes increases susceptibility to various types of infections. The most common sites are the skin and urinary tract. Dermatologic infections that occur with increased frequency in patients with diabetes include staphylococcal follicular skin infections, superficial fungal infections, cellulitis, erysipelas, and oral or genital candidal infections. Lower urinary tract infections and acute pyelonephritis are seen with greater frequency. A few infections, such as malignant otitis externa, rhinocerebral mucormycosis, and emphysematous pyelonephritis, occur almost exclusively in patients with diabetes. Infections such as staphylococcal sepsis occur more frequently and are more often fatal in patients with diabetes than in other individuals. In contrast, infections such as pneumococcal pneumonia have the same effect on patients with diabetes as they do on other persons.