When 30-year-old sales professional Nikhil Gupta (name changed) began experiencing mild bloating and stomach discomfort, he dismissed it as a routine gut problem, something he believed would pass with over-the-counter medication and a day’s rest. But in a city grappling with rising temperatures and relentless humidity, what seemed minor quickly turned serious.Within 48 hours, Gupta’s symptoms escalated to severe diarrhoea, repeated vomiting, dizziness and debilitating weakness. Unable to continue his daily work routine, he finally sought treatment at Zynova Shalby Hospital in Ghatkopar, where doctors diagnosed him with a heat-aggravated gastrointestinal infection. His daily schedule mirrors that of thousands of working Mumbaikars — long hours outdoors, travelling across neighbourhoods in peak afternoon heat, often skipping meals or relying on quick, roadside food. These outdoor stretches are followed by extended hours in air-conditioned offices, a sudden shift between extreme temperatures.“I did not hydrate myself. Initially, I ignored the early symptoms that were mild bloating, gas and abdominal cramps, which are often the first warning signs, doctors told me. I was treated with fluids, medication and rest, and discharged after two days,” says Gupta. Across Mumbai, hospitals and clinics are reporting a sharp rise in patients presenting with gastrointestinal complaints, loose motions, nausea, vomiting, abdominal discomfort and fatigue, with many cases linked directly to the ongoing heatwave.According to Dr Rishikesh Malokar, senior consultant gastroenterologist, hepatologist and therapeutic GI endoscopist at Zynova Shalby Hospital, the city is witnessing a nearly 50 per cent surge in stomach infections, particularly among those aged 30 to 45.Why heat stress leads to GI tract infection“High temperatures allow pathogens to multiply faster, leading to higher risks of food poisoning and spoilage. Chances of consuming contaminated water or food are higher. The body gets quickly dehydrated, weakening the gut lining and making it less capable of defending itself against harmful bacteria. This makes individuals more susceptible to infections that they might otherwise have resisted,” says Dr Malokar. In a city like Mumbai, where millions depend on street food, tiffin services or quick meals during long commutes, the risks are clearly amplified during summer.What worsens the situation, doctors say, is that many people underestimate their daily water needs, especially those working indoors. “There is a misconception that if you are sitting in an air-conditioned office, you do not need as much hydration. In reality, air conditioning can also contribute to dehydration if fluid intake is not maintained,” he says.The hidden stress of temperature swingsFrom stepping out into humid streets to entering chilled trains, buses, offices and malls, rapid temperature changes stress the body, affecting its immune system. “This makes individuals more vulnerable not only to stomach infections but to a range of heat-related illnesses,” says Dr Malokar.Story continues below this adExtreme temperature swings disrupt the gut barrier, changing the balance of gut bacteria. “This triggers inflammation, reduces nutrient absorption and can lead to symptoms like bloating, constipation, or diarrheal disease,” he adds.Also Read | How gut health is easy to restore with this 10-step guideHeat impact on the brainDr Akash Chheda, consultant neurologist at Zynova Shalby Hospital, says the brain is especially sensitive to temperature changes. “The brain relies on a stable internal temperature to function optimally. During extreme heat, the body struggles to maintain this balance. As dehydration sets in and blood circulation is affected, the brain may receive reduced blood flow and oxygen,” he explains. This disruption can manifest in a range of symptoms that many people may overlook or attribute to fatigue.“People may experience confusion, dizziness, light-headedness, headaches, irritability and reduced concentration. These are early warning signs that the body is struggling to cope with heat,” Dr Chheda says.In more severe cases, prolonged heat exposure can lead to heat exhaustion and eventually heatstroke, when the brain can swell, leading to neurological damage.Story continues below this ad“People tend to attribute initial symptoms to a viral infection when they are under acute heat stress. That’s why do not self-diagnose but consult a doctor,” says Dr Malokar.How to prevent heat stressBoth doctors advise people to drink at least 3–4 litres of fluids daily. Along with water, traditional drinks like coconut water, buttermilk (chaas) and lemon water (nimbu paani) can help maintain electrolyte balance. Outdoor activity should be minimised between 12 pm and 4 pm, when temperatures are at their highest. If stepping out is unavoidable, protective measures such as hats, scarves or umbrellas should be used.Freshly-cooked home food is safest during summer. Street food, cut fruits and ice-based items should be avoided unless hygiene is assured. While air conditioning offers relief, transition into a cold environment gradually. Wear loose clothing. Avoid strenuous exercise during peak heat. Early mornings or late evenings are safer.