You’ve used a heating pad on your lower back every night for months. One day you notice a lacy, net-like pattern on the skin there, reddish-brown, like a fishing net drawn on you. It doesn’t hurt or itch.
Doctors call this erythema ab igne, Latin for “redness from fire”. Most people know it as toasted skin syndrome.
What causes it
Repeated warmth that is too mild to burn you, but used for long periods on the same patch of skin, over weeks or months. The heat damages the small blood vessels just under the surface. They leak, and the skin stains in the pattern of the vessel network. That is why it looks like a net.
Common sources:
- Heating pads and hot water bottles used daily on the same spot
- Laptops resting on bare thighs
- Heated car seats and space heaters
What it looks like
- A mottled, net-like or lacy pattern
- Pink or red at first, turning brown or purplish over time
- Exactly where the heat source sits: lower back, tummy, thighs, shins
- Usually painless. Some people feel mild itching or burning.
Does it go away?
Early on, yes. Stop heating that area and the colour usually fades over several months. If you keep using heat on the same spot for a long time, the brown staining can become permanent.
Rarely, skin damaged this way for years can develop skin cancer. That is uncommon, but it’s the reason not to ignore the pattern.
The pattern can be a clue
Doctors pay attention to where the rash sits. A net-like patch on the tummy or back of someone who uses heat daily for pain tells them the pain is ongoing and severe enough to need constant heat. Long-standing abdominal or back pain deserves a proper check-up, whatever the heating pad is doing for it. If you’re in that position, a flare plan is a better answer than more hours on the pad.
How to prevent it
- Keep sessions to 15–20 minutes, with breaks of at least an hour. See how long to use a heating pad.
- Use the lowest setting that works.
- Keep a cover or towel between the pad and your skin.
- Move the pad around the area rather than on the same exact spot every time.
- Don’t fall asleep with it on. See sleeping with a heating pad.
- Check your skin once a week where you use the pad. If you have diabetes or any numbness, check every time.
- Take extra care if your skin is thin or prone to flaring. See eczema, psoriasis and fragile skin.
See a doctor if…
- You notice the net-like pattern anywhere you use heat.
- The patch develops a sore, a lump, a scaly spot, or a wound that won’t heal.
- You need heat every day for pain that has lasted more than a few weeks and nobody has checked the cause.
Before your next session, it’s worth reading who should not use a heating pad.
Clinically reviewed by: Nigel Chua (Hand Occupational Therapist) & Louise Yow (Physiotherapist). This article is general information, not a diagnosis. electricheatpad.com sells electric heat pads.
