harmful用作形容词的时候，表示有害的，尤其表示对健康或环境有害的，也有导致损害的，对...有害的等含义。

1.表示不良

Institutions have harmful effects on children.

收容机构对儿童有不良影响。

The high level of unemployment has produced harmful social consequences.

高失业率已经造成了不良的社会后果。

Hong Kong has issued safety warnings in connection with several TCMs contaminated with prescription only medicines and harmful impurities.

香港已经对中药处方药中有害物质的不良影响发出了安全警告。

2.表示不利

Studies have shown the harmful effects stress over exams have on children's health.

之前已有研究表明，考试压力过大对儿童的健康不利。

Under given conditions, the harmful can be transformed into the beneficial.

在一定的条件下，不利可以转化为有利。

3.表示对...有害的

We must not persist in pursuits harmful to the environment.

我们不应该坚持对环境有害的追求。

They also tested each ingredient for toxic effects – finding that none was harmful to

people.

他们也测试了药品成分的毒性，发现没有什么对人体有害的东西。