有害的(yǒu hài de) - harmful in Mandarin

有害的 (yǒu hài de) is harmful, built from 有害 (yǒuhài, to be harmful, literally "to have harm") with the attributive particle 的 (de) fixed on the end for use in front of a noun or after 是 (shì, to be).

You will see both forms in the wild: 有害 (yǒuhài) alone works as a predicate, 吸烟有害 (xīyān yǒuhài, smoking is harmful), while 有害的 (yǒu hài de) is what you reach for directly before a noun, 有害的气体 (yǒu hài de qìtǐ, harmful gas), or after 是 (shì) as in the examples here.

It is the opposite of 有益的 (yǒuyì de, beneficial) and sits close to 危险的 (wēixiǎn de, dangerous), though 危险 (wēixiǎn) leans towards immediate physical danger while 有害 (yǒuhài) covers slower harm, like pollution or an unhealthy habit.