Erythema ab igne, which means "red from fire," is a skin condition that occurs in response to heat exposure. Here are four things you need to know about erythema ab igne.

What are the signs of erythema ab igne?

If you have erythema ab igne, you'll notice pink, mottled patches on your skin. Over time, these patches darken and become red, purple, or brown. These darkened patches have a reticular pattern, according to NIH. Reticular is a medical term that means netlike. 

The patches don't usually cause any symptoms aside from their appearance, but some people experience symptoms like itching or burning. If you notice a rash that fits this description, make sure to show it to your dermatologist.

What causes erythema ab igne?

Erythema ab igne occurs in response to exposure to heat. This exposure doesn't need to be chronic, it just needs to be sufficient to heat your skin to between 43 and 47°C (109 and 116°F).

When your skin is exposed to high temperatures, both the epidermis (outer layer of skin) and the superficial blood vessels with your skin are damaged. The exact nature of this damage still isn't well understood, though researchers believe that moderate heat can denature the DNA of your squamous cells, the flat cells that make up your epidermis. "Denature" means that the double strands that make up your DNA split into single strands. 

Anything that heats your skin to the required temperature can lead to this condition, but laptops and heating pads are common culprits. If your laptop gets hot while in use, invest in a lap desk to protect your skin. If you're using a heating pad to soothe pain, use the low-heat setting. 

Is this condition serious?

Since the heat damages the DNA of your cells, cancers such as squamous cell carcinoma or neuroendocrine carcinoma can develop from the lesions, according to NIH. This can happen as many as thirty years after your erythema ab igne lesions first develop, so long-term follow up with a dermatologist is important.

Can it be treated?

If the source of heat is removed early enough, the rash may go away by itself. After prolonged exposure, however, the rash may become permanent. Your dermatologist can prescribe topical fluorouracil, a skin cancer drug, to help reduce the appearance of the rash.

If you develop a mottled rash after exposing your skin to heat, see a dermatologist. 

If you are worried about skin cancer, contact a doctor such as Henry E. Wiley, III, M.D. 

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