7 of your most-searched questions about hand warmers answered

Whether you’re embarking on a hike, or just stood watching your kids play sport, the cold can really get to your fingers. The best hand warmers, however, can keep them nice and toasty, whatever the weather throws at you. But there are a bewildering variety of hand warmers out there, so which is the right choice for you?

In this article, we’ll answer the most commonly asked questions about hand warmers, so you can get a better handle on what’s out there. We'll introduce the different types of hand warmer, explore how they work, and whether there are any potential dangers to using them. 

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What kinds of hand warmer are there?

There are many different kinds of hand warmer on the market today. The main types are chemical hand warmers, hand warmers that burn charcoal or lighter fuel, and battery-operated hand warmers.

There are two main types of chemical hand warmer. The first type is the air-activated hand warmer, which emits heat when exposed to the air. 

The second is the supersaturated solution (aka crystallisation-type) hand warmer, which involves a little more work on your part. You immerse this in hot water until it has absorbed the heat. Then when you wish to warm your hands, you click a metal disc in its centre, and the heat is released.

Lighter fuel hand warmers, as the name suggests, burn a type of specially produced lighter fuel. The flame is enclosed, and the device is usually wrapped in fabric to protect your skin from burning. Charcoal hand warmers work in a similar way; burning charcoal sticks in a special protective case.

Finally, battery-operated hand warmers generate heat through electric battery power, and are normally rechargeable via the mains. Some may offer other functions too, such as operating as a power bank and/or flashlight.

Are hand warmers reusable?

Air-activated hand warmers and charcoal hand-warmers are normally single-use only, making them bad for the environment, and more costly if you use them a lot. 

Supersaturated solution hand warmers, lighter fuel hand warmers and battery-operated hand warmers are usually reusable, making them more cost-effective and environmentally friendly options. 

How do hand warmers work? 

Air-activated hand warmers usually contain cellulose, iron filings, activated carbon, vermiculite and salt. When exposed to the air, heat is generated due to the oxidation of the iron filings. 

The supersaturated solution style (such as the Lifesystems Reusable Hand Warmer, shown above), works in a different way. It’s made by adding sodium acetate to cold water beyond the point where no more can be dissolved in it. 

When the hand warmer is heated, it allows the extra sodium acetate to dissolve into the water and crystallise. Then when the metal disc is bent, tiny particles of metal are released, which creates a chemical reaction that releases the stored heat energy from the solution.

Other types of hand warmer are more straightforward; either burning lighter fuel or charcoal sticks to create heat, or generating heat from battery power. 

Are hand warmers dangerous?

Everything is dangerous. Each year in the US alone, lawn mowers cause 75 deaths, 26 people are crushed to death by furniture, and six children die of suffocation from balloons. Set in that context, it’s theoretically possible for people to injure, or even kill themselves, through misuse of hand warmers. 

For example, filling a hand warmer with lighter fluid poses obvious hazards if you use the wrong type of fuel, or spill fluid in a dangerous environment. You could scald yourself when placing a supersaturated solution hand warmer in hot water. Or you could accidentally burn yourself when lighting a charcoal stick.

That doesn’t make hand warmers themselves dangerous. If they were, doubtless governments would swiftly ban them, or at least put restrictions on their sale. The main danger is in their misuse. 

Are hand warmers toxic?

Air-activated hand warmers are definitely toxic. If ingested, the iron filings they contain may cause vomiting, diarrhea, stomach bleeding and ulcers. If large amounts are ingested, symptoms may also include tremors, seizures, heart problems and kidney or liver failure. 

For this reason, it’s important to keep chemical hand warmers well out of reach of pets, who may try to eat them. And it’s not just animals you may have to worry about. This paper explores four cases of elderly people who accidentally ingested the content of disposable hand warmers. (All, thankfully, made full recoveries.)

Do hand warmers expire?

Chemical hand warmers normally come with an expiration date, just to keep the manufacturers covered. However, anecdotal evidence suggests that if properly stored, air-activated hand warmers can last months and even years after their use-by date in practice.

Are hand warmers endothermic or exothermic?

If a process absorbs energy (takes in heat), it is called endothermic and if it emits energy (gives off heat) it is called exothermic. It’s easy to see then, that chemical hand warmers release energy though an exothermic reaction. If they didn’t, they would be kind of pointless.