If something harmful is unchecked, it is continuing or increasing without or despite any limits or attempts to prevent it.

If current trends go/continue unchecked, obesity will become the number one cause of death in this country. 如果目前的趋势得不到遏制，肥胖将成为该国最大的死亡原因。

The war raged on, unchecked by the UN's efforts to stop it. 战火仍在蔓延，联合国的调停努力未能奏效。