For how long are individuals infectious after developing measles?

Individuals with measles are considered contagious from about 5 days before the rash appears until approximately 4 days after the rash has developed. This period reflects the time when the virus can be transmitted to others, meaning that they are infectious right before the rash appears and for some time after it has manifested.

The correct answer highlights both sides of this contagious period, emphasizing that individuals can spread measles shortly before the visible signs begin, which often leads to unrecognized transmissions within communities. This aspect is crucial in controlling outbreaks, as individuals may not realize they are infectious until the rash appears. Understanding this timeframe is essential for effective infection control and preventative measures during outbreaks.