Does Sunlight Kill Mold? What It Can Do and What It Can’t

Last Updated on October 26, 2026 by Umar Farooq

Does sunlight kill mold? Direct sun can dry out and damage mould on an exposed surface such as a cushion or a curtain, but it will not reach mould inside a material, it is weak through a window, and it does nothing about the damp that grew the mould. Your grandmother’s instinct to air things in the sun was not daft. It just has a short list of things it works on.

I have a soft spot for this one because it is the cheapest treatment going, and for once the evidence is not entirely against it.

Does sunlight kill mold? What the museum guidance says

Conservators handle mouldy textiles for a living, so I trust them over most cleaning blogs. The Western Australian Museum’s page on stopping mould growth says that the combined effects of ultraviolet light, heat and dryness can very effectively kill mould spores, and that growth can be significantly curtailed by simply airing an item out on a sunny day. For white household textiles it suggests about half an hour each side in summer and an hour each side in winter.

Note what is doing the work: not UV alone, but UV, heat and dryness together. I’d put the greatest weight on the dryness, because mould needs water, and the EPA’s rule is that it is important to dry water-damaged areas and items within 24-48 hours to prevent mold growth. That’s a drying deadline, not a mould timer, but it shows why moving air and sun are useful.

Why sun works on a cushion and not on a damp wall

Sunlight acts on what it lands on. A thin film of mould on the outside of a fabric is exposed; the threads inside a wall, a mattress or a plank of wood are not. The EPA’s position on porous materials is that absorbent or porous materials may have to be thrown away if they become moldy, and no amount of sun changes the fact that the growth sits inside them.

Dry mould is also paused, not removed. I explain what stays behind in does mold die when it dries out, and it applies to a sun-dried patch just as much as to one that dried on its own.

Does a sunny windowsill do the same job?

Not reliably. Indoor light is much weaker than strong direct sun, and I found no mould-specific figure for how much gets through glass, so I would not rely on it. A sunny room can also host mould: it is the cold, condensing glass and the damp sill that grow it, as I describe in mould around windows.

The related myth is that mould needs the dark. I looked at that in can mold grow in the dark: light matters far less than water.

Four steps for sunning a damp or lightly mouldy item

Brush loose mould off outdoors, not in the house, and wear gloves and a dust mask. If you are worried about your health, speak to a doctor. Strong sun can fade dyed fabric, so test a hidden corner first (general caution, not a measurement).

1. Fix the water source that made it damp, or it will be back within weeks.
2. Choose strong, direct sun and moving air, and a dry day. A damp, overcast one does little.
3. Expose each side for the museum’s suggested time: about 30 minutes in summer, an hour in winter for white household textiles.
4. Brush it off and launder or clean it afterwards. Dead or dry mould is still there.

For curtains in particular, mould on curtains goes through wash, treat or bin.

When to stop relying on the sun

If the mould is on a wall, in a mattress, inside upholstery foam, or over roughly 10 square feet (about 1 square metre), sun is not the tool. The EPA’s own cleaning method for hard surfaces is detergent and water, and for porous items it may mean replacement.

My opinion: use the sun to dry things, and use the dehumidifier to keep the room dry. The sun will not be there in January.

Use sun to dry things, and dry air to keep them that way

So, does sunlight kill mold? On a thin surface film on fabric, in strong direct sun, it helps. It does not reach inside materials and it does not fix the damp. Treat the sun as a good finishing move rather than the treatment itself.

FAQ

Does sunlight kill mold spores?

Strong direct sun with heat and dryness can kill mould spores on an exposed surface, according to the Western Australian Museum. It is not a guaranteed kill, and it won’t reach spores inside porous material.

Does sunlight kill black mold?

I haven’t found a reliable source that tests black mould specifically, and colour doesn’t identify species. Treat it the same way: sun may help on exposed fabric, but I wouldn’t rely on it, and large areas need proper cleaning.

Can mold grow in direct sunlight?

Yes, if the surface is damp. Light is far less important than moisture, which is why a wet windowsill in a sunny room can still grow mould.

Does sunlight through a window kill mold?

I couldn’t find a mould-specific figure, and indoor light is generally much weaker than direct outdoor sun. I wouldn’t count on it.

Can I put a mouldy mattress or cushion in the sun?

It may help dry the outside, but mould inside foam or filling won’t be reached, and the EPA says porous materials may have to be thrown away. For soft furnishings that stay damp, replacing is often the honest answer.