Erythema ab igne (EAI) is a distinctive skin reaction resulting from repeated, prolonged exposure to heat that is not hot enough to cause a traditional burn. This condition, often called “toasted skin syndrome,” develops when an area of skin is consistently subjected to infrared radiation from a heat source, such as a heating pad used for chronic pain relief. The resulting discoloration and net-like pattern are a direct consequence of this chronic thermal exposure. While EAI is a benign condition, managing it involves two steps: first, stopping the cause, and then addressing the resulting skin changes.
Identifying Erythema Ab Igne
Erythema ab igne presents as a characteristic net-like or lacy pattern on the skin, known as a reticulated appearance. The discoloration typically begins as faint pink or blotchy redness before progressing to patches of reddish-brown or darker hyperpigmentation. This specific pattern develops directly on the area of skin exposed to the heat source, such as the lower back, abdomen, or thighs, matching the shape of a heating pad or laptop.
The skin is repeatedly exposed to temperatures usually between 43 and 47°C, which is below the threshold for immediate thermal injury. This chronic, low-level infrared radiation causes damage to the basal keratinocytes and the superficial blood vessels beneath the skin’s surface. The breakdown of red blood cells leads to the deposition of hemosiderin, an iron-storage complex, and an increase in melanin pigment. These pigment deposits create the persistent, non-blanching, brownish discoloration that forms the characteristic lacy pattern.
Immediate Management Stopping the Cause
The first step in managing Erythema ab igne is the complete and permanent cessation of the inciting heat source. No treatment for the discoloration will be effective if the chronic thermal exposure continues. The skin requires a sustained period to cool down and recover from the ongoing damage.
Common culprits include the long-term, daily use of electric heating pads, hot water bottles, or electric blankets for chronic pain management. Other frequent sources are prolonged resting of a laptop computer directly on the skin or sitting very close to a space heater. For mild cases where the discoloration is faint and recent, simply removing the heat source may lead to complete resolution of the rash over several months. The erythema and hyperpigmentation can slowly fade once the chronic inflammatory stimulus is eliminated.
Treating the Skin Discoloration
Once the heat source is completely removed, the focus shifts to treating the residual hyperpigmentation, though expectations should be realistic. For cases that are mild and recent, the discoloration may spontaneously resolve within a few months, sometimes taking up to a year. Consistent application of simple emollients can help maintain skin barrier function as the area recovers.
For more pronounced or persistent hyperpigmentation, topical medications can be utilized to accelerate the fading process. Dermatologists may prescribe topical retinoids, such as tretinoin, which work by increasing the turnover of skin cells to help shed the pigmented epidermis. Another option is hydroquinone, a depigmenting agent that inhibits the enzyme tyrosinase, thereby reducing melanin production. Results with these topical treatments are often slow and require continued use over many months.
In long-standing cases where the pigmentation is deep and stubborn, advanced treatments like laser therapy may be considered. Lasers such as the Q-switched Nd:YAG or fractional non-ablative lasers are sometimes used to target the pigment that has settled deeper in the skin. This approach specifically addresses the dermal melanophages—cells that have absorbed the excess melanin and hemosiderin—helping to break down the pigment particles. Topical 5-fluorouracil cream has also been reported to help clear atypical cells that can develop in the affected area.
Professional Monitoring and Risk Assessment
Consulting a dermatologist is important to confirm the diagnosis and rule out other skin conditions that can mimic the net-like pattern, such as livedo reticularis. Professional evaluation is necessary if the rash is blistering, shows signs of skin thinning, or if the hyperpigmentation fails to show any improvement after six to twelve months of heat cessation. A dermatologist can also assess if the underlying reason for chronic heat application, such as persistent pain, needs further medical investigation.
Although Erythema ab igne is benign, a rare but significant risk exists for malignant transformation, particularly in long-standing, severe cases. The chronic thermal injury can lead to changes in the skin cells, increasing the risk of developing skin cancers, most notably squamous cell carcinoma. This risk is higher with EAI that has been present for many years.
Patients with EAI should be monitored long-term for any changes within the pigmented area. Immediate professional assessment is warranted if any new symptoms appear.
Concerning Symptoms
- Development of non-healing sores
- Ulcerations
- Firm nodules
- Areas of thickened, scaly skin
In suspicious cases, a skin biopsy may be necessary to microscopically examine the cells and definitively rule out malignancy.