Why Do I Get a Headache After Running? Causes, Dehydration and How to Stop It Happening
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Published September 2026 | Written by Andy Hood
Headaches after a run are more common than most runners realise, and if you've ever finished a long run feeling brilliant only for a dull ache to creep in an hour or two later, you're not imagining things. I've been here myself, especially after a long run in the middle of a training block. I'll look back over the session, swear I was hydrated enough going in and drank enough throughout, and still end up asking myself: was it dehydration after all?
Often, yes, it probably was. This article covers why running headaches happen, what the research actually says (kept light, I promise), and what's worked for me and other runners in preventing them.
Table of Contents
Why Do Runners Get Headaches After a Run?
There's actually a name for this in medical literature: primary exercise headache. It's a recognised condition, not something runners have made up, and it's specifically linked to strenuous exercise including running. The interesting part is that researchers still don't fully agree on why it happens. The leading theory is that it's vascular, meaning the blood vessels in and around your brain widen or narrow more than usual during hard effort, and that shift is what triggers the pain signal.
What we do know is that it tends to show up during or shortly after exertion, usually within half an hour of finishing, and it's been reported by runners, cyclists, weightlifters and rugby players alike. So if it's happening to you, you're in good company.
Here's the thing I found genuinely interesting when I looked into my own pattern. My running headaches tend to appear in the hours after a run, not during it, and they've never once shown up after a big event like a 100K or the Tour du Mont Blanc. They're far more common for me during a training block, around long runs or longer hard efforts.
That's not a coincidence. Race day usually comes with better fuelling, better hydration discipline, adrenaline, and a taper behind it. Training runs are where the small gaps in prep tend to catch up with you.
Dehydration and Running: The Sneaky Culprit
If there's one cause worth its own section, it's this one. Dehydration is consistently flagged as one of the most common triggers for post-run headaches, and it's sneakier than people expect.
I used to assume that if I felt fine while running, drank at reasonable intervals, and didn't feel especially thirsty, I must have been hydrated enough. But even on cooler days I was likely losing more fluid than I realised. Wearing warmer gear and extra layers in winter means you're still sweating plenty, but the chill on your face and hands lulls you into thinking you're cooler than you actually are underneath all that kit. You don't feel like you're overheating, so you don't think to drink as much, and the headache turns up later to tell you otherwise.
Signs of dehydration to watch for
The tricky part with dehydration is that the signs aren't always obvious mid-run. Keep an eye out for:
A headache that builds gradually in the hours after finishing, rather than sharp pain during the run itself
Dark yellow urine, or noticeably less of it than usual
Unusual fatigue that feels heavier than the effort should explain
Dry mouth or dry skin that lingers post-run
Feeling thirstier than normal well after you've finished
Muscle cramping, which often points to electrolyte loss alongside fluid loss, particularly sodium
Heat and altitude speed all of this up, but don't assume you're safe just because it's cold out. Cooler weather running, especially in layers, is one of the easiest ways to underestimate your fluid loss.
One thing worth clearing up, because it trips a lot of runners up: needing to urinate less, or not at all, during a long run isn't unusual and isn't itself a red flag. Hard effort naturally reduces urine production because blood flow is being prioritised elsewhere. What's more worth paying attention to is the opposite extreme, needing to urinate frequently throughout a long effort, which is more often linked to drinking more than your body needs relative to the sodium you're taking in, rather than to dehydration. If you notice urination picking back up late in a long run or ultra, that's usually your pace and effort easing off, not your hydration status tipping over.
Other Common Causes of Headaches After Running
Dehydration is the big one, but it's not the only cause. A few others worth knowing:
Low blood sugar. If you run first thing in the morning on an empty stomach, or run fasted regularly, a dip in blood sugar can trigger a headache. A small snack beforehand, even something light, can make a noticeable difference.
Heat and sun exposure. Direct sun and high heat are known headache triggers on their own, separate from dehydration, and UV exposure specifically can set off headaches in people who are prone to them.
Breathing patterns. Irregular or shallow breathing during hard efforts can throw off your oxygen and carbon dioxide balance slightly, which some runners feel as light-headedness or a building headache.
Neck and posture strain. Running form and everyday posture both play a part. If your head sits forward of your torso, whether that's from hunching at a desk or running with tension in your shoulders and neck, that muscular strain can contribute to tension-type headaches that flare up after exercise.
Caffeine and alcohol. Worth a mention because they're easy to overlook. Too much caffeine is linked to more frequent headaches over time, and alcohol after a run, especially before you've properly rehydrated, can make a headache worse rather than better.
How to Prevent Headaches After Running
This is the part I care about most. I'd much rather understand what's actually causing my headaches and head them off before they start, than reach for the medicine cupboard afterwards and just deal with the consequences.
Hydrate properly, not just during the run. Start hydrated the day before a long run, sip steadily throughout, and don't skip fluids after just because you've stopped sweating. This matters just as much in winter as summer. If you run in layers, treat that as a reminder to drink more, not less.
Watch your electrolytes on longer or harder efforts. Water alone doesn't replace what you lose in sweat. On longer sessions, an electrolyte drink or tablet can help, particularly if you're a heavy or salty sweater.
Eat before you run, especially in the morning. If you train fasted and get headaches afterwards, try a small carb-based snack beforehand and see if that changes things. It's a simple test that tells you a lot.
Warm up properly before hard efforts. Jumping straight into pace work or a long run without easing in puts more sudden demand on your body. A gradual warm-up gives your system time to adjust rather than being caught off guard.
Build intensity gradually across a training block. Sudden jumps in volume or effort are more likely to trigger these headaches than a steady, progressive build. If headaches tend to cluster around your hardest training weeks, that's worth looking at.
This is actually one of the reasons I train with Runna. It builds intensity and distance gradually and sustainably, with deload weeks built in roughly every four weeks, so you're not stacking hard effort on hard effort without a chance to recover. For readers of this blog, Runna is offering a free trial that's double the usual length, two weeks instead of one. Use code ANDY2 in the app, or grab it directly through this link.
Protect yourself from sun and heat. A cap, sunglasses, and running in the shade or during cooler parts of the day can all help if you know sun exposure is a trigger for you. Runna adapts for heat, a feature I use often especially when training abroad.
Check your posture and neck tension. If you spend most of the day hunched over a desk, that tension doesn't just disappear when you lace up. A bit of mobility work or simply being conscious of your running posture can help.
Keep an eye on caffeine and go easy on alcohol post-run. Small changes here, particularly if you're getting headaches often, are worth trying before anything else.
When to See a Doctor About a Running Headache
Most running headaches are harmless and fall into that "primary exercise headache" category, meaning there's no underlying issue behind them. But it's worth knowing when a headache after running deserves proper medical attention rather than home remedies. Speak to a doctor if:
It's your first ever headache like this and you're over 40
The pain comes on suddenly and severely, like nothing you've felt before
It's accompanied by confusion, vision changes, neck stiffness, or slurred speech
It doesn't improve with rest, fluids and food, or keeps recurring frequently
You have a personal or family history of any vascular or neurological condition
This isn't meant to alarm anyone. The vast majority of runners dealing with post-run headaches have nothing more sinister going on than dehydration, low blood sugar, or a training load that's ramped up a bit fast. But it's always worth ruling out anything else if things feel unusual or severe.
I'm not a doctor, just a runner with tens of thousands of miles behind me, so if you're ever in any doubt, please seek proper medical advice rather than taking my word for it. In the UK visit the NHS website for further information on headaches.
FAQ: Headaches After Running
Why do I get a headache after running but not during?
This is really common, and it's mine too. It's thought to be related to the delayed effects of dehydration, blood sugar dropping after the effort of the run has passed, or a slight lag in how your blood vessels settle back down after exertion. It's a big reason why post-run headaches can catch you off guard hours after you've already showered and moved on with your day.
Can dehydration cause a headache even in cold weather?
Yes, and it's one of the easiest things to underestimate. Wearing extra layers in cold weather means you're still sweating and losing fluid, but the cold air on your skin can trick you into feeling cooler and less depleted than you actually are. Treat winter runs with the same hydration discipline as summer ones.
Why don't I get headaches during races but I do during training?
This pattern is more common than you'd think. Race day usually comes with a taper, better sleep, deliberate fuelling and hydration strategy, and adrenaline that training runs simply don't have. Training block headaches, especially around long runs, often point to small gaps in day to day hydration or fuelling that races tend to paper over.
Should I take painkillers before I run to prevent a headache?
It's best to address the root cause first rather than reaching for medication as a default. Try improving hydration, fuelling before fasted runs, and warming up properly. If headaches are frequent and these changes don't help, that's a conversation for a doctor rather than something to self-manage with regular painkiller use.
Is a headache after running a sign I'm overtraining?
Not necessarily on its own, but if it's showing up consistently around your hardest or longest sessions, it's worth looking at your overall load, sleep and recovery alongside your hydration and fuelling. A cluster of headaches during a heavy training block is often your body flagging that something in the routine needs adjusting.
About the Author
I'm Andy, an ultra and endurance runner based in the UK, and founder of Check Ya Balls, a menswear brand raising awareness for testicular cancer. Running became my way of rebuilding after my own cancer diagnosis, and it's since taken me through multiple ultras, two crossings of the Tour du Mont Blanc, UTMB in Chamonix, and events like the Krispy Kreme London 50 and the Ultra Challenge South Coast 100. In 2027 I'll be adding the London Marathon to that list.
I train with
and work with coach Steve Middleton Lowes to build my blocks sustainably, and I write this blog to share what I learn along the way, the honest, practical stuff that actually helps, whether that's why your head hurts after a long run or how to get through your first ultra. When I'm not running, I'm usually fundraising for cancer charities close to my heart, currently working towards £50,000 raised.
You can read more about my running and my story on the About page, or head to the blog for more guides like this one.
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