No—rusty-looking stuff on the inside of the lid is not something you should ignore. If the inside of the can or lid is rusted, the safe advice is to throw the contents out and not taste it.

What to look for

  • Okay: a little surface rust on the outside that wipes off, and the can itself is otherwise intact.
  • Not okay: rust on the inside, heavy rust, leaks, bulging, deep dents on the seam or lid, or an off smell when opened.

For your tuna can

If you opened a Chicken of the Sea can in water and saw rusty material on the lid’s inside surface, the safest move is to discard it and not eat from that can. Rust on the inside suggests the lining may be compromised, which means the food could have been exposed to contamination.

Practical rule

When it comes to canned food, the rule is simple: when in doubt, throw it out.

TL;DR: inside rust = don’t eat it.