Think Before You Sprint: When is it Too Hot to Run?
Last week’s heatwave may have ended, but much of the UK is still basking in warm, dry conditions, with highs of 24–27°C forecast in parts of England this week. For runners, that means the question still stands: when is it too hot to run?
Even when the Met Office no longer classifies conditions as a ‘heatwave’, late summer temperatures can still put extra stress on your body when you run. Anything in the mid-20s or above requires you to adapt your pace, hydration, and clothing choices. The risk is not just about the thermometer reading. It’s how your body responds to heat and humidity. That’s why the same safety principles apply now, even with the heatwave behind us.
How to run safely in warm weather
1. Pick the coolest part of the day
In the UK summer, that’s usually early morning or later evening. The NHS and Met Office both recommend avoiding 11am–3pm, when the sun is most intense. Even a few degrees difference can make a big difference to your performance and, more importantly, recovery. You could also choose shaded routes, avoid dark asphalt (it retains heat, making you even hotter) and if you’re training for a race, use these sessions for easy miles rather than chasing PBs.
2. Hydrate before, during, and after
Hydration is important for runners all year round, but it’s a 24-hour job in hot weather. The UKHSA and NHS both recommend drinking more cold fluids, even if you’re not thirsty. If you’re out for over an hour, it’s always a good idea to add electrolytes to your water. They help your body to hold onto water and replace salts lost through sweat. In extreme heat, some runners lose over two litres of sweat per hour, so carry water with you and loop past your home or a shop if you need to top up.
3. Wear light, breathable layers
This is where your kit really comes into play! In hot weather, materials really matter. The problem with cheaper, heavier fabrics is that they can trap heat and hold onto sweat, making you feel hotter, much faster. Instead, your running kit should help sweat evaporate and let air circulate. It’s worth investing in technical fabrics.
4. Don’t skip the SPF
UV levels remain high during the late summer in the UK, which means sunburn can develop faster, even if there’s some cloud. Remember to apply SPF 30 or higher to any bare skin at least 20 minutes before going for a run. Plus, always reapply if you’re out for more than two hours. It’s also important to find a sweat-resistant formula so it stays on. It might seem like a faff before a run, but if you get sunburnt, you could be out of training for days while your skin heals.
5. Slow down your session
Heat makes your usual pace feel harder, because your heart and skin have to compete for blood flow to cool you down. England Athletics suggests adjusting once temperatures rise above 25°C, and I fully agree. Slow down your pace and, on the hottest days, swap intervals for an easy run, shorten your distance or split a long run into two shorter runs.
6. Watch for warning signs of heatstroke
Dizziness, chills, confusion and nausea are red flags for heatstroke. If you’re feeling unwell during your run, stop, find shade and hydrate as soon as possible. NHS guidance makes it clear that heatstroke is a medical emergency, so if you (or someone else) have hot, dry skin or feel disoriented, always seek out medical help. Don’t assume fitness protects you from heat stroke. In reality, active people are on UKHSA’s list of higher-risk groups in extreme heat.
7. Cool down gradually
Tempted to jump straight into a cold shower after your run? It’s not a good idea. Sudden temperature shocks can stress out your system. Instead, aim to cool yourself down slowly. Keep walking for a few minutes post-run, slowly sip on water and use a cool (not cold) shower or damp towel on your neck to bring your temperature down gradually.
Warm weather has become the norm in the UK during summer, but you don’t need to miss out on runs. If you adapt your training and prepare properly, you can still enjoy training safely. That means planning your timing, pacing yourself and most importantly, knowing when to call it a day.
Written by Oliver Carter, Marketing Manager at Ronhill