Something bites me at night but I can’t find it. What is it?

Waking up with new bites and finding nothing is maddening. The honest answer is that bites alone rarely tell you what did it. Bed bug, flea and mosquito bites can look much the same, and some itchy marks are not bites at all. The way to find out is to catch the culprit, so it can be named. And if the bites spread, blister or you feel unwell, see a doctor.

If only you are getting bitten, that does not mean you are imagining it. People react to bites very differently. Two people can share a bed, and only one of them gets itchy marks.

The usual suspects

• Bed bugs. Bites on skin that was exposed while you slept: arms, neck, shoulders, face. Look for dark spots and pale shed skins in mattress seams. See our bed bug guide.
• Fleas. Often around the ankles and lower legs, but anywhere if a pet shares the bed. Fleas can live in carpets left by a previous owner’s pet, so having no pets does not rule them out. Our page on fleas without pets covers that.
• Mosquitoes. Exposed skin, a whine near your ear, more in warm months and near water. See our mosquito guide and bites with the windows shut.
• Spiders often get the blame, but they rarely bite people. A bite alone does not prove a spider did it. Our spider guide explains more.
• Not a bite at all. Skin conditions, heat rash, or a reaction to a new washing powder can look like bites. A doctor or pharmacist can tell the difference.

How to catch it

1. Fit interceptors under each bed leg. These cups catch bed bugs climbing up. Pull the bed away from the wall and keep the bedding off the floor, so the legs are the only way up.
2. Check the bed in the morning with a torch. Seams, piping, the headboard and the frame joints.
3. Put sticky monitor traps along the skirting next to the bed and under it. They catch fleas and other crawling insects.
4. Try the white sock test for fleas. Pull long white socks over your trousers and walk slowly around carpets and rugs. Fleas show up as dark specks that jump.
5. Comb your pet over white paper with a flea comb. Dark specks that turn reddish on damp kitchen roll are flea droppings.
6. Keep a short diary. Where the bites are, which room you were in, a photo each day. Patterns help a professional or a doctor.
7. Keep anything you catch. Press it onto clear tape on white paper and photograph it next to a coin.

The cat is on flea treatment. Could it still be fleas?

It can be. Treating the pet deals with fleas on the animal, but eggs and young fleas can still be in carpets and soft furnishings, and they keep hatching for a while. Hoover often, wash pet bedding, and ask your vet whether the treatment you use covers the home too. Follow the label on any home flea product, and keep pets out of treated rooms for as long as it says.

Can you have just one flea?

A single flea can hop off a visitor’s dog or come in on your clothes from outside, and never become a problem. But if you see one, check for more with the sock test and traps for a couple of weeks. Bites that keep coming point to more.

See a doctor or pharmacist if bites spread, blister, become warm, swollen or weepy, or if you have a fever or feel unwell. If your face or throat swells or you struggle to breathe, get emergency help straight away. If you are pregnant, or it is a baby being bitten, check with a doctor before using any insect product.

When to call a professional

Once you have caught something, the next step depends on what it is. Bed bugs and a heavy flea problem are worth a professional. Mosquitoes usually need screens and a look at standing water nearby. If you have searched and trapped for a few weeks, found nothing, and the bites continue, our page on still being bitten when no bed bugs are found covers what to try next.