When it comes to describing someone or something that is easily affected or influenced by external factors or stimuli, the phrase "sensitive to" is often used. However, there are several alternative phrases and words that can be used to convey a similar meaning. Some examples include "responsive to," "attuned to," "affected by," "susceptible to," "empathetic towards," "sympathetic to," and "in tune with." Each of these phrases conveys the idea that something or someone is capable of detecting and responding to certain stimuli or emotional cues. Using a variety of synonyms can help to keep your writing fresh, concise, and nuanced.