Healthy Food Delivery : Those Tiny Lines in Your Mug Could Be a Hidden Health Risk

I think we all have a bowl or mug like this in our cupboard or pantry. It looks normal on the outside. Inside, though, there are faint lines snaking across the inside like tiny stretch marks or scratches. Turns out, those lines inside your coffee mug may signal a problem called “crazing.”

A recent Reddit post asked about these mysterious markings, and several commenters noticed the distinct crazing pattern. While seeing someone else with a mug like this might make you feel a little better about your favorite coffee drinking vessel, it shouldn’t ease your mind that it’s normal or safe to use. Here, we’ll explain what crazing is, what causes it, and how to prevent it.

What Is Crazing?

Crazing is a pattern of hairline cracks that form in the glazed surface of ceramic drinkware and bowls. Unlike its appearance would indicate, it’s not caused by scratches from spoons or cleaning pads. It’s actually caused by the ceramic expanding or contracting at different rates during heating and cooling. That includes very hot or cold drinks and the cleaning process, either by hand or in a dishwasher.

Sometimes, determining what a scratch is and what is crazing isn’t immediately obvious. However, there are signs to look for.

While scratches usually run in straight or random directions and feel slightly raised, crazing forms a web-like pattern that sits beneath the surface glaze. The lines often appear darker because coffee or tea seeps into the cracks over time.

Also, a food-safe glaze should feel smooth and glass-like. If the interior surface appears dull, uneven or marked with faint intersecting lines, the glaze may have started to craze.

It is worth noting that some decorative pottery intentionally uses a similar look, which is not the same as crazing.

Is Crazing Dangerous?

Yes. The smooth glaze on the mug or bowl provides a protective barrier against moisture and residue from soaking into the ceramic. Once crazing begins, that barrier breaks down, potentially trapping liquid, coffee oils or food particles that regular washing may not fully remove. Bacteria or mold can settle into those tiny cracks.

So, should you throw out a mug with crazing? Most experts recommend retiring heavily crazed items from food or drink use, as it’s simply not worth the risk. You might think you can adequately clean it after each use, but the harmful bacteria might be beyond reach and can pose a health risk.

If the mug holds sentimental value, you don’t have to (immediately) get rid of it. Instead of using it as a drinking or eating utensil, you can repurpose it as planters, a pen or pencil organizers, decor, storage for small items, or something else purposeful.

It’s better to be safe than sorry, even if it is your favorite mug or bowl.

How To Prevent Crazing From Happening Again

Crazing can’t be fixed or reversed, so it’s better to practice safe habits to protect your ceramic items.

With rapid temperature changes posing the biggest risk for crazing, don’t pour boiling liquid into a cold mug or one straight from the cabinet. Also, make sure it’s dishwasher safe before putting it into a machine and don’t use extremely hot water if washing by hand.

While you can’t fix the mugs you already have, replace any cracked items with drinkware that meets modern manufacturing standards. Look for items that are labeled food-safe or lead-free.