Final answer:
The redness around a wound caused by harmful bacteria is due to inflammation, an immune response that involves blood vessel dilation, increased blood flow, and white blood cells combatting the infection.
Step-by-step explanation:
When harmful bacteria invade a wound, the skin around the wound turns red due to a process called inflammation. This biological response is the body's second line of defense against pathogens. Inflammation is triggered by the release of chemicals when skin or other tissues are damaged. These chemicals cause blood vessels to dilate, increasing blood flow and making the area red and warm.
The influx of blood also delivers white blood cells like neutrophils to the wound site, and these cells help to combat the bacterial invaders. A well-known agent in this process is histamine, which not only contributes to the dilation of blood vessels but also helps attract immune cells to the site of injury. This inflammatory response helps to establish a physical barrier against the spread of infection and begins the process of tissue repair.