Lactose Intolerance and Tummy Ache: Causes, Symptoms, Testing, and Relief

If milk, a latte, or a scoop of ice cream keeps ending in a crampy, gassy tummy-ache, you’re probably wondering whether lactose is the culprit. Here’s the short version: lactose can trigger pain and bloating when your gut doesn’t break it down properly. The good news? You don’t have to ditch all dairy forever, and you can confirm what’s going on without endless guesswork.

TL;DR: The lactose-tummy ache link in plain English

• Lactose is milk sugar. If you don’t make enough lactase (the enzyme that digests it), lactose gets fermented by gut bacteria, making gas and drawing water into the bowel. Cue cramps, bloating, wind, and sometimes diarrhoea.
• Symptoms usually start 30-180 minutes after dairy and depend on dose and what else you ate. Hard cheese and butter are low in lactose; milk and ice cream are higher.
• To check: try a 2-week low-lactose trial, then reintroduce in measured amounts. You can also ask for a hydrogen breath test through the NHS in some areas.
• Don’t confuse it with a milk allergy (which can involve hives, wheezing, or swelling). If you get those, seek urgent help.
• Relief is practical: adjust portions, choose lactose-free dairy, use lactase tablets, and keep your calcium and iodine intake on track.

How lactose triggers pain: what’s going on in your gut

Start with the basics. Lactose is the main sugar in milk from cows, goats, and sheep. Your small intestine normally makes lactase, the enzyme that splits lactose into glucose and galactose so you can absorb it. If lactase is low, undigested lactose drifts into the large intestine. There, resident bacteria feast on it. Fermentation creates hydrogen, methane, and short-chain fatty acids. This gas stretches the gut, which can feel like tight, crampy pressure. Meanwhile, lactose also pulls water into the bowel, which can mean looser stools.

The classic symptom cluster? Bloating that builds like a balloon, lower abdominal cramps, lots of wind, audible gurgling, and sometimes urgent diarrhoea. Nausea happens for some. Pain often starts 30 to 180 minutes after eating dairy and eases once gas passes or a bowel movement happens. The sensation can be sharp or dull, on one side or across the lower belly-tummy-ache is the catch-all most people use.

Why does it hit some people and not others? Most humans globally are “lactase non-persistent,” meaning lactase levels naturally fall after weaning. In the UK, it varies by ancestry. White British people have lower rates than many parts of the world, but lactose intolerance still shows up in GP clinics, and it’s more common in people of East Asian, African, Middle Eastern, and South Asian descent. NHS and British Dietetic Association materials both describe this pattern. There are also “secondary” causes-lactase can dip for a while after a gut infection, with coeliac disease, inflammatory bowel disease, or after small intestinal surgery. Very rarely, there’s a congenital form present from birth.

Here’s the useful part: symptoms are dose-dependent. Many people tolerate small amounts (say, a splash of milk in tea) but react to a large milkshake. Food structure matters too. Milk is high in lactose per serving. Yogurt often causes fewer symptoms because live cultures help break down lactose. Hard and long-aged cheeses are very low in lactose-cheddar, Parmesan, and Emmental are usually fine in modest portions.

To make it practical, think in grams. A typical 250 ml glass of cow’s milk has about 12 grams of lactose. A 30 g slice of cheddar has barely any. A 150 g pot of live yogurt sits somewhere in the middle. Your threshold might be around 6-12 grams in one sitting, but it varies. Eating lactose with a meal slows gut transit a bit and can soften the blow.

That’s the engine behind the tummy-ache. Fermentation makes gas; osmosis pulls water. Your gut’s stretch sensors don’t love either. If you also have IBS, you can be more sensitive to that stretch, so the same amount of gas feels more painful. NICE guidance on IBS notes this sensitivity, and dietitians often use lactose adjustments before broader FODMAP changes.

Is it lactose intolerance, milk allergy, or something else?

Not all milk trouble is the same. Sorting this out saves you months of unneeded restriction-and avoids missing something serious.

• Lactose intolerance: digestive only-bloating, cramps, wind, diarrhoea. Starts within a few hours of lactose. No skin or breathing symptoms. Often dose-related.
• Milk allergy (IgE-mediated): can involve hives, lip/tongue swelling, wheeze, vomiting, and can be dangerous. It can start minutes after dairy, even with tiny amounts. If you’ve had these symptoms, treat it as an allergy and seek urgent medical advice.
• Non-IgE cow’s milk protein allergy (more common in infants): skin and gut symptoms that are delayed. Needs GP/paediatric dietitian input.
• IBS: can overlap-gas and pain after lactose are common if IBS is present, but IBS also reacts to other FODMAPs (like fructans and polyols). If lactose is only part of the story, this may be why.
• Coeliac disease: can reduce lactase when the gut lining is inflamed. If you have ongoing symptoms, iron deficiency, weight loss, or a family history, ask your GP about coeliac blood tests before changing your diet.
• Gut infections and post-infectious changes: after gastroenteritis, lactase can dip temporarily. Symptoms often improve over weeks as the lining heals.

Red flags that point away from simple lactose issues and need a GP appointment: unintentional weight loss, nocturnal diarrhoea (waking from sleep to open bowels), blood in stool, persistent vomiting, fevers, a new change in bowel habit after age 50, or dehydration-especially in children or older adults. UK GPs follow NICE pathways for these signs; don’t wait it out if any apply.

Quick reality check: A2 milk (with only A2 beta-casein) is not a lactose fix. It still contains lactose. Some people say it feels gentler, but if lactose is the problem, A2 won’t remove it. Plant milks naturally don’t contain lactose, but check they’re fortified-calcium and iodine matter in the UK diet.

What to do next: tests, swaps, supplements, and a simple plan

Here’s a structured way to pin it down and feel better without giving up nutrition or joy.

Step 1: Run a focused 2-week trial

1. For 14 days, keep lactose low but don’t go extreme. Use lactose-free cow’s milk and yogurt, choose hard cheeses, and limit high-lactose foods like regular milk, soft cheeses, ice cream, and creamy sauces.
2. Keep a simple symptom diary: what you ate, time, symptoms (0-10 scale), and timing. Note stress, coffee, spicy food, and artificial sweeteners, so you don’t blame lactose for something else.
3. If symptoms clearly ease, move to Step 2. If there’s no change at all, lactose probably isn’t the main driver-consider IBS or other causes and speak with your GP or a registered dietitian.

Step 2: Reintroduce to find your personal threshold

1. Choose one lactose source at a time. Day 1: 100 ml milk (about 5 g lactose). Day 2: 200 ml. Day 3: 250 ml. Stop at the first amount that sparks symptoms. That’s your current ceiling.
2. Test yogurt on a separate week-live cultures help, so your ceiling might be higher. Test ice cream another week, ideally after a meal.
3. Use what you learn. Many people handle small amounts across the day but not a big hit at once.

Step 3: Confirm, if needed

• Hydrogen breath test: Available in some NHS clinics and privately. You drink a lactose solution; if your breath hydrogen rises and symptoms appear, that supports the diagnosis.
• Blood lactose tolerance test: Less common now. Measures your blood glucose after lactose; a flat response suggests malabsorption.
• Infants: Stool acidity and reducing substances tests can help-this is specialist territory. If a baby has poor growth or severe symptoms, see a GP/health visitor.

Step 4: Eat well without the aches

• Pick low-lactose dairy: hard, long-aged cheeses (cheddar, Parmesan, Gruyère) are usually well tolerated. Butter is almost lactose-free. Lactose-free cow’s milk and yogurt are easy UK supermarket finds.
• Portion pairing: have lactose with a meal, not on an empty stomach. Slower transit, fewer fireworks.
• Lactase supplements: Tablets or drops can break down lactose in a meal. Start with the manufacturer’s dose for about 10-13 g lactose (a glass of milk) and adjust to your response. Keep them in your bag for cafés and trips.
• Plant-based milks: Go for fortified options. In the UK, look for calcium (~120 mg/100 ml) and iodine on the label. Pea, soy, and oat milks are common. Taste and protein content vary-soy and pea are higher-protein.
• Mind the nutrients: If you cut back dairy, plan calcium, iodine, riboflavin, and B12. Good non-dairy sources include small bony fish (sardines), eggs, calcium-set tofu, fortified plant milks and yogurts, and some leafy greens. UK iodine can be tricky if you don’t eat dairy or fish-check fortified milks and consider advice from a dietitian if you’re pregnant.

Fast label-reading in UK shops

• “Lactose-free” dairy has the lactose broken down but still gives you dairy protein and calcium.
• “Milk” in the allergen list doesn’t tell you lactose content; it tells you there’s milk protein. Look for specific claims like “lactose-free” or “low lactose.”
• Words that often signal lactose: milk, whey, milk powder, milk solids. Ghee is very low in lactose, but if you’re extremely sensitive, check brand info.

Rule-of-thumb decision guide

1. Symptoms after dairy only in the gut, dose-related, no skin or breathing issues → likely lactose intolerance. Try the 2-week plan.
2. Symptoms include hives, swelling, wheeze, or faintness → possible milk allergy. Stop dairy and seek medical advice urgently.
3. Symptoms happen with lots of foods including wheat, onion, certain fruits → consider IBS/FODMAP patterns and ask a dietitian about a structured approach.
4. Red flags (weight loss, blood, persistent night-time symptoms) → contact your GP.

Lactose content at a glance (typical servings)

Numbers vary by brand and process, but the pattern is consistent: milk and ice cream are the big hitters; hard cheese and butter are easy wins.

Checklist: getting comfy fast

• Swap your daily milk to lactose-free or fortified soy for two weeks.
• Keep hard cheese; park soft fresh cheeses for now.
• Keep lactase tablets in your bag for meals out.
• Eat lactose with meals, not on an empty stomach.
• Hit calcium and iodine: check labels for fortification; include fish or eggs if you eat them.
• Note symptom timing in a diary; reintroduce to find your ceiling.

Mini‑FAQ

Can I ever “fix” it? Some secondary cases resolve-after gastroenteritis or when coeliac disease is treated. Primary lactase non-persistence is genetic, but many people expand tolerance by starting low and building up, letting the gut microbiome adapt.

Why can I eat cheese but not drink milk? Aged cheeses have most of the lactose drained with the whey during cheesemaking, then bacteria consume more as the cheese matures. Milk keeps all its lactose.

Is goat’s or sheep’s milk better? They still contain lactose in similar amounts. Some people find them easier, but that’s usually taste, fat structure, or protein differences-not lactose.

What about probiotics? They can help some people with gas and bloating, but effects are strain-specific and modest. Live yogurt is a practical way to test this in food form.

Can kids be lactose intolerant? Yes-especially after tummy bugs. In babies, true primary lactose intolerance is very rare. If a child has poor growth, blood in stool, or severe eczema/wheeze with milk, see your GP.

Troubleshooting by scenario

• Barista drinks set you off: Ask for lactose-free cow’s milk or fortified soy/oat. If you want regular milk, take lactase with the first sip and have food alongside.
• Cheese boards are fine, but pizza hurts: The mozzarella and the milk in the base sauce are higher lactose; try a thin slice, choose mature cheeses, or use lactose-free mozzarella.
• Holiday tummy: After a gut bug, back off lactose for 2-4 weeks, then reintroduce slowly. Consider a temporary lactase supplement.
• Pregnancy or breastfeeding: Don’t self-restrict heavily without checking your calcium and iodine plan. Ask your midwife/GP for a dietitian referral if you’re unsure.

Why this stands up

The mechanism (low lactase → lactose fermentation → gas and water) is described in NHS patient information and gastroenterology texts. NICE guidance recognises symptom overlap with IBS and supports diet-led management. The British Dietetic Association provides practical food lists showing relative lactose amounts in dairy. Large population studies show variable prevalence by ancestry, explained by inherited lactase persistence. If you want a formal test, hydrogen breath testing is the clinical standard in many UK centres.

One last tip: tweak, don’t nuke. Most people don’t need to ban dairies; they need to right-size lactose and use smart swaps. Start with milk changes, keep your favourite cheeses, test your limits, and keep life tasty and comfortable.

Key term used in this guide: lactose intolerance.