The UK is currently sweltering under extreme temperatures, with much of the country under a red warning for heat. The mercury could creep up to 40°C in some places, and people are being urged to stay sensible in the high heat.

One of the most important things to remember in a heatwave is to stay hydrated. If you’re sweating more in the hot weather, you need to replenish that liquid to ensure you don’t become dehydrated. But how can you tell the difference between dehydration and regular thirst?

James Morehen, sports nutritionist and hydration expert at the electrolyte brand Vidrate, has revealed the hidden signs of dehydration to watch for, and how to tell when it’s gone too far.

How to tell if you’re dehydrated

It’s not easy to tell if you are dehydrated. The signs can be quite subtle, so it’s important to keep an eye out.

James said: “Dehydration signs aren’t always obvious, they can show up as a headache or difficulty concentrating.

“This can be mistaken for tiredness or screen fatigue, but if you experience either during hot weather, it can be an early sign your body needs more fluids.”

Certain cravings can also signal dehydration. If you find yourself reaching for salty or sugary food, it could be a sign your body is struggling.

James explained: “When fluid levels drop, it can lead to fatigue, which the body may interpret as hunger.”

The third sign, which can be unpleasant both for you and the people around you.

James explained: “Persistent bad breath can sometimes be an overlooked sign of dehydration. When you’re not drinking enough fluids, your body produces less saliva, which plays a key role in washing away bacteria in the mouth.

“As bacteria build up, it can lead to an unpleasant odour, so staying well hydrated can help support better oral health as well as overall hydration.”

What’s the difference between thirst and dehydration?

Thirst is actually a late sign of dehydration. By the time you start to feel thirsty, it’s already in effect. That’s why it’s important to regularly sip water throughout the day to stop yourself getting too dehydrated.

James said: “Drinking a full glass of water when you wake up and before you go to bed is one of the best things you can do during hot weather.

“Your morning glass helps to rehydrate after a night of sweating, and a glass before bed can help regulate body temperature – just leave a gap of 30 to 45 minutes before sleep to avoid a disrupted night.”

You should also keep drinking water throughout the day.

How much water should I be drinking?

James said: “It is recommended to drink six to eight glasses of water a day but during hot weather, but in hot weather this can increase to around three litres, especially if you’re active or spending time outdoors.

“A simple way to check if you’re hydrated enough is by checking your urine colour. You should aim for a pale-yellow colour, if it’s darker than that, you likely need to consume more water.”

A GP has revealed how people can prevent chafing and heat rash as Britain’s latest heatwave drives temperatures skyward, with scorching highs of 40C predicted. Heat alerts have been extended as some parts of England and Wales experience exceptionally hot and humid conditions.

Certain regions could see temperatures climb to 40C on Wednesday and Thursday owing to a “heat-dome” positioned over western Europe, triggering extreme weather throughout the continent. As millions nationwide grapple with the heat and heightened health concerns, including skin complaints, Dr Robert White has outlined how people can minimise their risk of chafing and heat rash and address them.

Skin chafing is an uncomfortable irritation caused by friction between skin surfaces or between skin and rough materials. It commonly develops in warm, moist areas, including the inner thighs, groin, armpits, and nipples.

When perspiration and moisture are present, they can soften the skin. This can make it more susceptible to tearing and breaking down with repeated rubbing.

Dr White is a General Practitioner with an Extended Role (GPwER) specialising in Dermatology and Skin Surgery. He is the joint Clinical Lead for the NHS East Kent Community Dermatology Service, reports the Mirror.

Dr White said: “Chafing is a common skin irritation caused by repetitive friction from skin rubbing against skin or clothing. It most frequently occurs between the thighs, under the arms, beneath the breasts, or in the groin area, especially during physical activity or in hot, humid conditions.

“Complications include redness, burning, or stinging sensation. In extreme cases, this can result in blistering of the skin. Broken skin can also lead to bacterial or fungal skin infections. In chronic cases, darkening of affected skin can occur (hyperpigmentation).”

Dr White recommends keeping the affected area clean and dry while applying Sudocrem to establish a protective ‘barrier’. He also recommends other creams, adding: “Application of a barrier cream such as Sudocrem, Vaseline or Cicaplast will help, or a natural anti-inflammatory cream such as Aloe Vera. You can also take a short course (five to seven days) of a mild topical steroid such as hydrocortisone 1% cream.”

To tackle the issue before it arises, he recommends steering clear of tight-fitting clothing and opting for breathable materials, such as cotton or moisture-wicking synthetics. He explained: “Applying lubricants before exercise can reduce friction. And wearing tight clothing for exercise (such as thigh bands or compression shorts) also minimises chafing.”

When left untreated, chafing can change from a slight annoyance to a big health issue because of several reasons, like the chance of infection, serious physical trauma, and worsening situations.

According to Dr White, those who tend to perspire heavily or are unaccustomed to hot climates and suddenly find themselves on a sweltering holiday may also be more prone to heat rash. He said: “Heat rash (also called prickly heat or miliaria) happens when sweat gets trapped in blocked pores, causing inflammation and irritation.

“It’s especially common in hot, humid weather and is more commonly seen in areas where the skin rubs against skin or clothes. The best treatment for heat rash is to cool the skin and keep the area dry.

“Application of anti-itch creams such as calamine lotion or anti-inflammatories such as hydrocortisone cream (for a few days only) can also help. Avoid ointments or oil-containing topical products, as these block pores and can make the situation worse. Oral antihistamines can help reduce severe itch.”

He went on to say: “As ever, prevention is better than cure, wear loose-fitting clothing in light and moisture-wicking fabrics. And if you are somebody who is prone to heat rash, minimise exertion when in hot environments and keep well hydrated.”