What do systemic reactions affect in the body?

Systemic reactions have a widespread effect on the body rather than being localized to a specific area. When a substance is ingested or absorbed, it can enter the bloodstream and trigger a response that affects multiple organ systems simultaneously. This can result in symptoms such as changes in heart rate, blood pressure, or even neurological function, depending on the nature of the substance and the individual's overall health.

In contrast, the other options imply localized effects. For example, the first option suggests that reactions only affect the skin at the site of contact, which does not account for the broader implications that systemic reactions can have. The second option focuses solely on a specific organ, disregarding the potential for multiple organ involvement. The fourth option mentions only the muscles around a burn area, which again misses the comprehensive impact that systemic reactions can have on overall body functioning. Through this understanding, it's evident that systemic reactions fundamentally alter general body function following the ingestion or absorption of substances.