How to tell if you have bed bugs: the definitive guide

Bed bugs are notoriously difficult to detect. They're tiny, they hide during the day, and their bite marks mimic dozens of other skin conditions. If you suspect you have them, relying on bites alone is a mistake — by the time the infestation is large enough to produce obvious bite patterns, it has usually been established for weeks or months.

Here's how to actually confirm a bed bug infestation, in order of reliability.

1. Blood spots on bedding

The most common early sign is small rust-brown spots on your mattress, fitted sheet, or pillowcase. These are caused when a feeding bed bug is crushed during sleep, or when partially digested blood passes through an engorged bug as it moves away. Look along the seams and tufting of your mattress, and at the hemline of your fitted sheet.

Fresh spots will be reddish-brown. Older spots oxidise to dark brown or black. If you find multiple spots in a cluster, that's a strong indicator.

2. Shed skins (cast nymphal shells)

Bed bugs go through five nymphal stages before reaching adulthood, moulting their skin at each stage. These translucent, empty husks accumulate in hiding spots and are one of the most reliable physical signs of an active infestation. They look like a hollow, pale version of the bug itself.

Check: mattress seams, the wooden slats of your bed frame, behind the headboard, inside bedside table drawers, and along skirting boards near the bed.

3. Dark faecal stains

Bed bug faeces appear as tiny dark dots — similar to a felt-tip pen dot — on surfaces where bugs congregate and defecate over time. Unlike blood spots, these smear when wet. You may find them on the mattress, on the bed frame timber, on wallpaper near the bed, or inside plug socket faceplates (a surprisingly common hiding spot).

4. Live bugs

Adult bed bugs are about the size of an apple seed (4–5mm), flat, oval, and mahogany brown — though they swell and turn red-brown after feeding. Nymphs are smaller and paler. They're most active in the two hours before dawn but can be found hiding during the day if you know where to look.

• Mattress seams and the piping around the edge
• The joins in wooden bed frames, especially where sections slot together
• Behind and underneath the headboard
• Inside and around bedside tables and lamps
• Behind loose wallpaper and picture frames close to the bed
• Inside electrical sockets and light switches near the bed
• In the folds of curtains and along curtain rails

5. The smell (if the infestation is advanced)

A large, well-established infestation produces a faint but distinctive sweetish, musty odour — often described as overripe raspberries or coriander. If you notice this smell in your bedroom without an obvious explanation, treat it as a serious warning sign and inspect thoroughly.

What about bite marks?

Bites are a helpful early clue but not a reliable confirmation. Around 30% of people have no visible reaction to bed bug bites at all. Others react in ways that are indistinguishable from mosquito bites, flea bites, or allergic reactions. The pattern (typically in a line or cluster on exposed skin) is suggestive, but physical evidence from the bed itself is what confirms an infestation.

What to do next

Don't try to treat it yourself with over-the-counter sprays. Consumer insecticides are largely ineffective against bed bugs (many UK populations have developed resistance to pyrethroids) and — more importantly — they disperse bugs into the walls and neighbouring rooms, making professional treatment harder and more expensive.

Get a professional quote. Heat treatment is the gold standard — it kills all bed bugs at all life stages, including eggs, in a single visit without chemicals. Use our free matching service to get connected with a vetted local specialist.