As temperatures continue to fall over the winter months, many people will be reaching for a hot water bottle to take to bed and even have around the house.
The boiling water devices can be a cheaper alternative to turning on the heating for a prolonged period of time, but they do come with some health risks.
Dr Amir Khan has warned that the warming appliance could leave you with a skin condition called "erythema ab igne".
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Speaking on ITV's Lorraine, Dr Amir said: "It's the time of year when you'll be dusting off your water bottle.
"Particularly because of the heating prices, you might not want to turn your heating on, so you turn to your old water bottle," reports Express.
While the warming rubber can keep you toasty and comfy, you shouldn't be pressing it against your skin for too long.
The doctor continued: "You can get a rash with hot water bottles if you apply them to your skin for a long period of time.
"I see this quite a lot - it's got a bit of a posh word, it's called erythema ab igne or the hot water bottle rash.
"If you put your hot water bottle against your skin, you get this kind of a wavy, red rash on your skin.
"It does fade after time if you take the hot water bottle away, but it does look quite serious when you have it."
This type of rash is characterised by mottled-looking skin, with some hot water bottle users complaining of mild itchiness and a burning sensation.
Once you identify this red rash, you should stop using your water bottle on the area.
The rash usually disappears within a few weeks or months if your skin is only mildly affected.
However, severe pigmentation caused by the bottle could mean marks will stay on your skin for some years, according to Now Patient.
Fortunately, treatment with a topical cream called tretinoin or laser may improve the appearance.
Hot water bottles aren't the only culprits that can lead to erythema ab igne as other heat sources like heated car seats or laptops can also lead to the rash.
The tricky thing about this type of rash is that it's triggered by non-painful heat, so you might not realise you're putting yourself at risk.
However, this isn't the only hidden danger of using water bottles. Dr Amir also warned that they could burn your skin severely if they burst.
If you haven't used your hot water bottle in a while, the doctor recommended checking it first before putting it near your body.
"If it's an old one you haven't used for ages, fill it up first and give it a good squeeze because you need to make sure it's in a good condition," Dr Amir said.
There have been cases of old hot water bottles exploding, which could lead to "severe burns", according to the doctor.
For example, Helen Cowell, 45, was using a hot water bottle to tackle back pain when it perished and left her with burns on her legs and bottom earlier this year.
"So check your hot water bottle. Give it a good squeeze," Dr Amir added.
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