Street food has an irresistible charm: it's affordable, tasty, and often tied to local culture. However, behind the tempting aroma and rich sauces sometimes lie hidden risks, especially when it comes to the quality of ingredients used. One common culprit in many cases of gastrointestinal and oral discomfort is low-quality or repeatedly used cooking oil. A lesser-known but significant concern is its potential link to mouth ulcers and allergic reactions.
Low-quality oils, particularly those reused multiple times in street food stalls, often degrade and oxidise with heat, Dr Sudha Desai, MD Physician at Ruby Hall Clinic, Hinjawadi, Pune. “This process forms harmful compounds like free radicals, trans fats, and acrolein, the known irritants to the digestive and oral linings. These substances can irritate the mucous membranes and may lead to mouth ulcers and other inflammatory reactions in vulnerable people,” she adds.
Many of these oils are either poorly regulated or mixed with cheaper substitutes and synthetic additives. In extreme cases, non-edible elements may be blended in to reduce costs. “This kind of adulteration doesn’t just affect digestion. It can also trigger immune responses, especially in people with food sensitivities or weaker gut health. Prolonged consumption can cause chronic inflammation, disrupt the gut lining, and lower immunity, thus causing frequent mouth sores and allergic flare-ups,” says Dr Desai.
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Mouth ulcers, also called aphthous ulcers, are painful lesions on the inner cheeks, lips, or under the tongue. While emotional stress, vitamin deficiencies, or trauma are common causes, dietary factors often act as the tipping point. Spicy sauces and acidic condiments prepared with low-grade oil can irritate the delicate tissues in the mouth. “When these oils are heated repeatedly, they release toxins that can damage the cells lining the mouth. For people already prone to ulcers, this can make them more frequent and harder to heal,” explains Dr Desai.
Moreover, oxidative stress from poor-quality oil can weaken the mucosal barrier and trigger localised inflammation. This can be especially problematic for children, the elderly, or anyone with a sensitive digestive system.
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Allergic reactions and inflammatory responses:
Low-quality cooking oils often come loaded with other problematic substances. Artificial flavouring agents, preservatives, MSG, and food colorants are common in street sauces. “Together, they can lead to skin flare-ups, swelling, breathing difficulties, or even severe allergic reactions in sensitive people,” says Dr Desai.
Another problem, she warns, is the high omega-6 content in many cheap seed oils like sunflower or palm oil. Says she, “An imbalance between omega-6 and omega-3 fats contributes to long-term systemic inflammation. These oils can worsen eczema, food intolerances, and even joint inflammation.” Slowly, these reactions take a toll on the immune system, making the body more reactive to even small dietary triggers.
You can follow these prevention tips suggested by Dr Desai:
- Observe cooking practices: If the oil looks black or gives off a burnt smell, it’s a red flag. Walk away.
- Choose freshly cooked items: Grilled, steamed, or roasted options are usually safer than fried food.
- Limit sauces: Ask for sauces on the side or skip them if you know you're prone to allergies or ulcers.
- Stay hydrated and eat cooling foods: This helps balance internal acidity and soothes the digestive tract.
- Pay attention to your body: If you frequently get ulcers after eating out, consider eliminating suspicious foods for a while.
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