Verbseoul.
하다 verb (adj)
유해하다yuhaehadato be harmful, noxious, injurious

To say to be harmful, noxious, injurious politely in the present tense, use 유해해요 (yoo-hae-hae-yoh). Below is the full conjugation of 유해하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
유해해
yoo-hae-hae
유해해요
yoo-hae-hae-yoh
유해합니다
yoo-hae-hahm-nee-dah
Past
유해했어
yoo-hae-hae-ssuh
유해했어요
yoo-hae-hae-ssuh-yoh
유해했습니다
yoo-hae-hae-sseum-nee-dah
Future
유해할 거야
yoo-hae-hahl- -guh-yah
유해할 거예요
yoo-hae-hahl- -guh-yae-yoh
유해할 겁니다
yoo-hae-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
유해하세요
yoo-hae-hah-sae-yoh
Suggestion / Let's Polite (요)
유해해요
yoo-hae-hae-yoh
Question Polite (요)
유해해요?
yoo-hae-hae-yoh-?
Connective “and” — (고)
유해하고
yoo-hae-hah-goh
Conditional “if” — (면)
유해하면
yoo-hae-hah-myuhn
Noun form — (기)
유해함
yoo-hae-hahm