“Seriously concerning”: Redditor shares photo of mold under sink to r/whatisit, discovers it’s toxic

A Redditor turned to r/whatisit after spotting something unsettling growing under their kitchen sink.

Reddit reacts to the discovery

Some commenters thought it might be “some kind of wet rot” or even “mushroom mycelium,” warning that a water leak was almost certainly behind it.

Others were more spooked, with one person saying it looked like “some eldritch horror thing” that belonged in a creepypasta thread.

But the top comment, which the original poster pinned, took a serious tone. “This is seriously concerning. Based on the image, the growth you’ve found is likely a type of fungi, specifically a dry rot fungus,” one person wrote.

They explained that the “root” or branch-like structures are rhizomorphs, a signature feature of dry rot species like Serpula lacrymans.

According to the commenter, these rhizomorphs can transport water and nutrients over long distances, allowing the fungus to spread through wood and even masonry.

“The presence of this type of growth in a cabinet, especially near a sink, indicates a significant and persistent moisture problem,” they continued. “It’s not just a surface issue; it means the underlying wood is actively decaying. This can cause severe structural damage to your home.” Their final piece of advice was not to try to handle it alone, and call a professional immediately.

Why dry rot is dangerous

Dry rot isn’t just another form of mold. As AXA Insurance explains, it can reduce once-solid beams, floorboards, or joists to “crumbling ruins.” It spreads fast, and if left untreated, the price tag for repairs can soar into the thousands.

If you find dry rot, they recommend removing any infected wood as soon as possible. Even nearby timber that looks healthy should be treated with a fungicide, since the fungus often spreads further than what’s visible.

In more severe cases, the fungus can move into brick or stonework. If that happens, plaster and mortar need to be removed until a full metre beyond the last sign of fungal growth. After repairs, good ventilation is key. Dehumidifiers, extractor fans, and even just keeping curtains open can help keep humidity levels in check.