“起保护作用”常见的英文表达有“play a protective role”“serve a protective function” 或 “act as a protective measure” 等，具体使用哪个表达可根据语境和习惯来选择。以下为你举例说明：
例句：The ozone layer plays a protective role by absorbing harmful ultraviolet radiation from the sun.
翻译：臭氧层通过吸收太阳有害的紫外线辐射而起保护作用。
例句：Certain nutrients in fruits and vegetables serve a protective function against various diseases.
翻译：水果和蔬菜中的某些营养成分对各种疾病起保护作用。
例句：The safety helmet acts as a protective measure to prevent head injuries in construction sites.
翻译：安全帽在建筑工地起到保护作用，可防止头部受伤。