Most people think they know the answer — but food-safety experts say this is one of the most misunderstood fridge rules out there.

Here’s the truth:

Tuna salad is a high-risk food because it’s made with ingredients that spoil quickly: tuna, mayo, eggs, celery, and sometimes onions. Once mixed together, bacteria can grow much faster than you’d expect.

So how long is it safe?
According to food-safety guidelines, tuna salad should only be kept for:

3 to 4 days MAX in the refrigerator

– Stored at 40°F (4°C) or below
– Kept in an airtight container
– Never left sitting out for more than 1–2 hours

After day 4, the risk of bacterial growth — especially Listeria and Salmonella — increases sharply, even if it still smells fine.

That’s why you feel uneasy eating it after day 3 — your instincts are actually right.

What about keeping it for a full week?

Food scientists say this is not recommended at all.
Day 5–7 puts it firmly into the “unsafe zone,” even if the bowl looks and smells normal.

Signs it’s gone bad:

• Watery or separated texture
• Sour smell
• Metallic or “off” taste
• Slimy coating
• Gas bubbles forming

Even mild changes mean the bacteria has already begun its work.

Bottom line:

If you want to meal-prep tuna salad safely:

• Make smaller batches
• Eat within 4 days
• Or freeze the ingredients separately (tuna freezes well — mayo does not)

Your sister may like to stretch a bowl for a week, but the experts say that’s not safe — and you’re right to avoid it after day 3.