In the ramshackle lanes of a south Delhi slum, Afshana Khatoon crouched wearily on her haunches and began lighting a small pile of firewood.

She had only just returned from six hours spent trudging through the urban forests and dry parks of India’s capital looking for kindling to turn into a makeshift stove. As the unforgiving summer heat soared above 40C, she had walked for miles, piling the sticks and fallen branches into a bundle on her head while sweat ran down her face.

Just a few weeks ago, the 35-year-old had been preparing meals for her four children on a small gas stove with little fuss. But as the crisis in the Middle East has choked India’s vital supplies of imported liquefied petroleum gas (LPG) – used by more than 60% of the country’s population for cooking – refills have been scarce and prices have risen far beyond what is widely affordable.

Khatoon, like growing numbers of people in India and more widely across Asia, has been forced to cook with crude, dirty fuels such as firewood and coal in order to survive. “It already feels like hell,” she said, as she bustled about, filling a pot with water. “I’m not eating properly, and I have to work much more than before. My whole day now is about collecting firewood and cooking.”

The return to fuels such as firewood and coal is not only deepening the economic strain of the war on ordinary civilians in countries across Asia, but raising concerns about public health, air pollution and the fragility of the energy transition.

India imports about 60% of its LPG needs, of which about 90% usually comes through the strait of Hormuz, the critical shipping route still blockaded amid the ongoing conflict between Iran and the US. Official data shows India’s LPG consumption fell by 2.2m tonnes in April, the sharpest decline in years.

As the war has dragged on, cooking gas prices in informal markets have surged. In Khatoon’s dimly lit shanty, her 5kg gas canister sat empty and forlorn in the corner. She said LPG had become prohibitively expensive for her family, rising to more than four times what she used to pay. “My husband earns 400 to 500 rupees a day. We can’t spend 1,000 rupees just on gas for a week,” she said.

While the Indian government insists there is no shortage, in a speech this week the prime minister, Narendra Modi, called on people to adopt austerity measures including limiting their use of fuel and petrol. According to the defence minister, India has petroleum gas reserves to last just 45 days.

Once Khatoon’s fire stove is lit, thick smoke rises from the flames. It stings the eyes and throat but she has no option but to breathe it in as she cooks. She put her head in her hands, admitting she felt utterly exhausted. “We just want to cook as quickly as possible,” she said.

Delhi already ranks among the world’s most polluted cities, and years of policy have focused on promoting cleaner fuels such as LPG and compressed natural gas to reduce emissions.

Environmental activists fear years of progress toward widespread use of cleaner fuels is being reversed as the war in the Middle East drags on. With shortages deepening, authorities in Delhi have temporarily relaxed restrictions on the use of coal and firewood.

“When prices rise, it’s the poorest who are forced to switch back to biomass,” said Harjeet Singh, a climate activist and the founding director of the Satat Sampada Climate Foundation. “Biomass burning is a major source of fine particulate pollution. In dense urban areas, the impact is even more severe because of how closely people live and how poorly ventilated these spaces are.”

Over the past decade, the Indian government has distributed more than 100m subsidised cooking gas canisters. But the current crisis is exposing a deeper fault line: access did not guarantee affordability, with families now forced to choose between food and fuel.

For many families, the gas cylinder has become, Singh said, “a symbol of a transition they can no longer afford to sustain”.

Thousands of miles away in the Philippines – where 90% of the country’s LPG needs are dependent on supplies flowing through the strait of Hormuz – a similar crisis has been playing out.

In a dingy alleyway in the capital, Manila, Josephine Songalia sat quietly by a charcoal-lit stove, fanning it until a flame appeared. A few months ago, she would have turned a knob to light the LPG powering her stove. But gas has become an unaffordable luxury for cooking here too. Prices for a small tank of LPG have tripled to about Php600 (about $9.80 or £7.20).

Compounding the crisis, the cost of food in the Philippines has also increased because of the ripple effects of the war, meaning that her family has no choice but to skip meals. “In the morning, my kids say: ‘Mama, we’re hungry.’ I tell them we don’t have food – just drink coffee,” she said.

Consumption of LPG in the Philippines has dropped 30% compared with the same period last year, as people have switched to charcoal owing to cost pressures. In a bid to ease the growing financial burden, the government has suspended the excise tax on LPG and paraffin for three months.

“At stake right now is the health of families … air pollution indoors will be proliferating,” said Mylene G Cayetano, a professor of environmental science and meteorology at the University of the Philippines, Diliman.

Cayetano said production of cheap charcoal was a “very dirty process”. The practice, mostly carried out in seaside or riverside areas, fills the air with ash and smoke and causes environmental devastation.

Back in the Delhi slum, as evening fell and the firewood stoves began to be lit to cook dinner, Shanti, 75, struggled for breath. She has been diagnosed with a chronic lung condition but has been forced to cook on firewood again for the past two months. “A doctor told me to stay away from smoke,” she said, coughing. “But what choice do I have? My health is getting worse but I need to eat.”