You turn on the bathroom light at night and something small and silvery darts across the tiles. It moves fast, it has no wings, and it disappears into the gap behind the skirting board before you can look twice. If that sounds familiar, you have silverfish, and learning how to keep silverfish out of bathroom spaces in the UK is easier than most people expect.
Silverfish do not bite, they do not spread disease, and they are not a sign that your home is dirty. They are a sign that your bathroom is damp. This guide explains what they are, why they choose bathrooms, and gives you a practical plan built on three things: cutting the dampness, sealing their hiding places, and removing what they eat. Follow the steps in order and most bathrooms are silverfish free within a few weeks.
What Are Silverfish and Why Do They Love Bathrooms
The silverfish is a small wingless insect, usually between 10 and 15 mm long, with a body covered in tiny silvery scales. It has long antennae at the front and three bristle like tails at the rear. Its common name comes from the way it moves, with a wriggling motion that looks like a fish swimming. They are nocturnal, so you will almost always see them at night when you switch on a light.
Silverfish need damp air to survive. They thrive when relative humidity sits between 75 and 95 percent, which is exactly what a bathroom becomes after a hot shower. Condensation on the mirror, a wet bath mat left on the floor, and steam with nowhere to go all push the humidity into the range they love. They also eat starches and sugars found in paper, wallpaper paste, cardboard, book bindings, and even cotton and silk, so bathrooms with stored magazines, cardboard boxes, or peeling wallpaper are doubly attractive.
One important reassurance: silverfish are harmless to people and pets. They do not bite or sting. The damage they cause is to your belongings, not to you. Chewed book pages, yellow stains on wallpaper, and nibbled edges on stored fabrics are the classic signs of a long standing colony.
How to Keep Silverfish Out of Bathrooms in the UK: The Three Part Plan
The most common mistake people make is treating the silverfish while ignoring the dampness that draws them in. Spray a few, catch a few, and new ones simply take their place because the bathroom still feels like home to them. The plan below works because it reverses that order: dry the space first, block the hiding places second, and remove the food third.
Most of these fixes cost little or nothing, and all of them are rental friendly, meaning no drilling or permanent changes are needed. If you rent, check your tenancy agreement before doing anything structural, but everything here is reversible.
Part 1: Cut the Dampness
Dampness is the root cause. Get your bathroom humidity down and you remove the one thing silverfish cannot live without. Aim to keep relative humidity below 50 percent where you can, and never let the bathroom stay steamy for long after a shower.
Run the extractor fan properly
Most UK bathrooms have an extractor fan, but most people switch it off too soon. The fan needs to run during your shower and for at least 20 to 30 minutes afterwards. That long run on is what pulls the steam out of the air instead of letting it settle on the walls, tiles, and ceiling. If your fan is noisy, old, or weak, that is worth fixing, because a bathroom fan is your first line of defence. Cleaning the fan grille every few months also helps, since dust buildup can cut airflow dramatically.
Damp air is behind more than one household nuisance. If condensation is a wider problem in your home, our guide on how to stop condensation on windows overnight covers the same principles room by room.
Fix the vents and open the window
Check that your bathroom vents are not blocked by dust, fluff, or paint. A vent that is sealed shut might as well not exist. If you have an openable window, cracking it open for 15 minutes after a shower makes a real difference, even in winter. Cold air holds less moisture, so a short burst of ventilation dries the room faster than you might expect.
Use a dehumidifier in stubborn cases
If your bathroom has no window and a weak fan, a small portable dehumidifier can transform the situation. Place it just outside the bathroom door with the door open, or inside the bathroom if it is rated safe for that use. Empty the tank regularly, or choose a model with a continuous drain hose if emptying it feels like a chore. In older UK homes with solid walls and poor airflow, a dehumidifier is often the single most effective purchase you can make against damp loving pests.
Change your bath mat habits
This is the simplest fix on the list and one of the most overlooked. A soggy bath mat left flat on the floor after every shower keeps a patch of the floor damp for hours, which is a perfect daytime hiding spot for silverfish. Hang the mat over the side of the bath or on a rail after every use so it dries fully, and wash it regularly. One recent survey found that a large number of people rarely wash their bath mats, which tells you how easy this one is to neglect.
Part 2: Seal the Hiding Places
Silverfish spend the day squeezed into narrow cracks and gaps, then come out at night to feed. Blocking those daytime hiding places makes your bathroom far less comfortable for them.
Seal skirting boards and cracks
Walk around the bathroom and look for gaps where the skirting board meets the floor or the wall, cracks in old grout, and gaps around the bath panel. A tube of bathroom sealant or decorators caulk closes most of these in an afternoon. Focus on the areas where you have actually seen silverfish run, since those are the gaps they are using. Let the sealant cure fully before the next shower, following the drying time on the tube.
Seal around pipes
Pipe entries are classic silverfish highways. Check where the basin, bath, and toilet pipes pass through the floor or walls. If there are visible gaps, fill them with sealant or expanding foam made for the job. This also helps with draughts, so it is rarely wasted effort.
Part 3: Remove What They Eat
Silverfish feed on carbohydrates and starches: paper, wallpaper paste, cardboard, book bindings, and natural fabrics. A dry bathroom with nothing to eat is a bathroom they will leave alone.
Start by clearing out any cardboard boxes stored in or near the bathroom. Replace them with sealed plastic containers if you need the storage. Move books, magazines, and paper files out of the bathroom entirely, since the humidity damages them anyway. If your wallpaper is old and peeling, that is both a food source and a hiding place, so repairing or replacing it does double duty. Vacuum along skirting boards and behind the toilet regularly to remove the dust, shed skin cells, and paper fibres they feed on.
Natural Deterrents That Genuinely Help
Once the dampness is under control, natural deterrents can add a useful extra layer. Be honest with yourself about what they can do: these are helpers, not cures. None of them will fix a damp bathroom on their own.
Lavender is the most widely recommended option. Silverfish dislike strong scents, so a few drops of lavender oil on cotton balls placed in corners, or a small lavender sachet in a bathroom cabinet, can make the space less inviting. Cedar is another traditional choice: cedar blocks or a little cedar oil work on the same principle. Cinnamon and citrus scents are also reported to help.
One product worth knowing about is diatomaceous earth, a fine natural powder that damages the waxy coating on insects. If you use it, buy the food grade version and apply it only as the label directs, in thin lines along skirting boards and behind fittings, never scattered loosely where children or pets can reach it. And skip the random powders and sprays recommended on forums unless the label is clear about what is in them and how to use them safely.
Traps: A Simple Way to Check Whether It Is Working
Traps do two jobs: they catch the stragglers and they tell you whether your plan is working. Simple sticky traps placed along skirting boards and behind the toilet are the easiest option. Check them once a week. If catches fall steadily over two to three weeks, your plan is working.
A classic homemade option is the rolled newspaper trap. Lightly dampen a rolled up newspaper, secure it with an elastic band, and leave it in the bathroom overnight. Silverfish crawl inside to feed and hide, and in the morning you seal the whole roll in a bag and put it in the outside bin. It will not solve an infestation by itself, but it is a cheap way to reduce numbers while the main fixes take effect.
What About Bleach and Boiling Water
You may have seen advice to pour bleach and boiling water down bathroom sinks to stop silverfish. Here is the honest version: this can kill the ones living in the drain and clear the organic buildup they feed on, and it is fine to do occasionally with care. What it cannot do is change the humidity of your bathroom. If the room stays damp, new silverfish will keep arriving no matter how clean the drains are. Treat it as a supporting step, not the main event.
Mistakes That Keep Silverfish Coming Back
If you have tried to get rid of silverfish before and they returned, one of these is usually the reason. Treating the insects while ignoring the damp is the biggest one, by far. Drying laundry on a radiator inside a small bathroom with the door closed is another classic, since it pumps huge amounts of moisture into exactly the wrong room. If you must dry clothes indoors, read our guide on how to stop clothes smelling damp when drying indoors to do it without creating a damp problem.
Other common mistakes include leaving the extractor fan off because it is noisy, storing cardboard boxes in the bathroom, and giving up after a week. Silverfish live for two to eight years and lay eggs in hidden crevices, so allow a full two to three weeks of dry conditions before you judge the results. Consistency beats intensity here.
When to Call a Professional
Most silverfish problems are solved with the plan above. Call a pest control professional if you are still seeing large numbers after a month of proper damp control, if they are damaging valuable books, documents, or fabrics, or if the dampness itself will not budge, which can point to a leak, failed grout, or a ventilation problem that needs a tradesperson. A professional can also identify whether you are actually dealing with silverfish or a lookalike such as the firebrat, which prefers warmer spots near boilers and hot pipes. If you are dealing with other household pests too, our guide on how to keep mice out of garden sheds shows the same seal and remove approach applied to a different invader.
Frequently Asked Questions
Are silverfish harmful to humans or pets
No. Silverfish do not bite, sting, or spread disease, and they are not poisonous if a pet eats one. They are a nuisance and a risk to paper, books, wallpaper, and natural fabrics, not to your health.
What attracts silverfish to bathrooms
High humidity is the main draw. Bathrooms regularly reach the 75 to 95 percent relative humidity range that silverfish need to thrive. Leaky pipes, poor ventilation, wet bath mats, and stored paper or cardboard make a bathroom even more attractive.
Will silverfish go away on their own
Almost never. As long as the bathroom stays damp and there is food available, they will stay and breed. The good news is that drying the space out reliably drives them away, since they cannot survive long in dry air.
Does lavender oil really repel silverfish
Lavender, cedar, cinnamon, and citrus scents can help deter silverfish as part of a wider plan, because the insects dislike strong smells. But scent alone will not fix the problem. Think of it as a supporting measure alongside damp control and sealing, not a replacement for them.
How long does it take to get rid of silverfish
With consistent damp control, sealing, and trapping, most people see a clear drop in numbers within two to three weeks. Because eggs can hatch over several weeks, keep the routine going for at least a month to be sure the colony is gone.
Conclusion
Learning how to keep silverfish out of bathroom spaces comes down to one insight: they are there for the dampness, not for you. Dry the bathroom properly after every shower, fix the vents, hang up the bath mat, seal the cracks and pipe gaps, and clear out the paper and cardboard they feed on. Add lavender or cedar as a finishing touch and use simple traps to confirm the numbers are falling.
None of this requires harsh chemicals or a big budget, just consistency for a few weeks. Start with the extractor fan tonight, and your bathroom will soon be a place silverfish no longer want to live.
