Antioxidants work by bolstering the body's defenses against potentially dangerous substances called free radicals.

It likely evolved as a defense mechanism against harmful substances.

The attendant, citing rules against flammable substances, barred the delivery.

This kind of protection is still "proof" against many non-invasive substances, such as anthrax.

The immune system is the body's defense against foreign substances, such as bacteria or viruses, that may be harmful.

Many women believe that the placenta acts as a shield against harmful substances.

The immune system normally protects the body against harmful substances, such as bacteria and viruses.

Problems with latex rubber include allergic reactions and poor protection against such substances as solvents.

We need to gather together all the forces for good in the battle against harmful, addictive substances.

Equally important, the discrimination against harmful substances doesn't work in this case.