What Is an Upper Respiratory Infection?
2. How Does a URI Happen?
The body has numerous defenses to inhibit the invasion of viruses and bacteria. Physical barriers, such as the hair follicles in the nose, are the first line of defense against pathogens. The immune system also plays a key role in warding off the spread of infections.
Even with defense systems in place, viruses and bacteria are successful in infiltrating the body due in part to their own adaptations. Many pathogens, for example, produce toxins or adhere to the mucus membrane, making it less likely they will be destroyed. It can take anywhere from one to 10 days between invasion and symptomatic expression.
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