A 9-year-old girl presents with a painful blistering patch on her right leg noted when her mother picked her up from school following an after-school ski club trip.
Diagnosis: Second-degree burn
When the mother helped the girl remove her boot to check the leg, she noticed a bright erythematous patch with blistering to the lateral distal lower extremity that had been covered by her sock. Her mother noticed that the girl had a disposable toe warmer in her sock, next to her bare skin. The girl had activated the toe warmer and placed it inside of her sock near her toes prior to putting on her boots and skis. She did not experience any pain until after she was done skiing, about 2 hours later.
On exam, the patient was in no acute distress and her vital signs were normal. She described her pain level in the right leg as 5 out of 10. The right, lateral distal lower extremity had an area of mild erythema with a central, intact, round 1.5-cm bulla and grouped, smaller adjacent vesicles proximal to the lateral malleolus. The area of erythema was blanching and minimally tender. She had full range of motion of the right ankle and foot, and her gait was intact.
The patient was diagnosed with a second-degree burn triggered by the disposable toe warmer in her sock.
Disposable chemical hand or foot warmers generally are composed of iron, activated carbon, salt, and vermiculite. When the iron is exposed to oxygen, it begins to oxidize and produce heat. Salt helps catalyze the reaction; the activated charcoal helps disperse the heat; and the vermiculite helps insulate the heat. These warmers can reach temperatures as high as 165°F if exposed to an oxygen-rich environment, such as shoes with ventilator holes.
Precautions for the warmers advise that they should not be exposed to free-flowing air, applied directly to bare skin, and used in shoes for vigorous activity such as running, or burns may occur. Supervision is advised for use in children or the elderly, who have relatively thin skin and may not apply them properly.1
In spite of these precautions, hand and foot warmers are useful tools for protecting hands and feet from cold injury and are generally regarded as safe. There are few references in the medical literature regarding injuries related to disposable chemical hand or foot warmers. One case report notes burns sustained by a diver using foot warmers while using nitrox as a breathing gas.2 Another series of reports involve ingestion of chemical disposable warmers by 4 elderly patients.3 These patients did not experience any serious consequences from the ingestion. However, no case reports were identified involving a pediatric injury from one of these warmers.
The patient in this case had apparently placed the warmer inside her sock next to the plantar surface of her foot, and it subsequently migrated to the thinner skin along the lower leg. Burns can be classified as superficial (first degree), partial thickness (second degree), or full thickness (third degree). Burns are also classified as minor, moderate, or severe. A minor burn in a pediatric patient is a superficial or partial thickness burn that involves less than 5% of the total body surface area (TBSA) in a patient aged younger than 10 years; is an isolated injury; does not involve the face, hands, perineum or feet; is not circumferential; and does not cross a major joint line.4
This patient had a minor burn and was a good candidate for outpatient care. Silvadene cream (silver sulfadiazine) was applied and the area was bandaged. The burn healed gradually without complications.
1. Littlehottieswarmers.com. (2019). Precautions : Little Hotties Warmers. [online] Available at: https://www.littlehottieswarmers.com/precautions [Accessed 5 Nov. 2019].
2. Anderson, GP. Skin Burns as a Result of using Commercial Hand Warmers in a Dry Suit Using Nitrox as a breathing gas. A Case Report. UHM Journal. 2008 Nov;46(9):900-4.
3. Tam AY, Chan YC, Lau FL. A case series of accidental ingestion of hand warmer. Clin Toxicol (Phila). 2008;46(9):900-4.
4. Sheridan RL. Burn Care for Children. Pediatr Rev. 2018;39(6):273-286.