Many everyday health habits are widely believed to support your well-being — but experts say some of them may be doing more harm than good. While these routines are often followed without question, new research suggests that not all common advice holds up under close examination.
A major analysis of thousands of studies found that some of the most trusted medical recommendations are based on outdated or incorrect assumptions. In several cases, large clinical trials have shown the exact opposite of what doctors and patients long believed to be true — revealing that even well-intentioned guidance can turn out to be wrong.
A common household habit doesn’t actually prevent asthma attacks
For decades, medical groups advised families to keep their homes spotless to protect against asthma. The theory seemed straightforward: removing dust mites, mice and cockroaches would limit allergic reactions and help reduce flare-ups, especially in children.
However, research has shown this advice doesn’t hold up. In a major study, families with children sensitized to mouse allergens underwent intensive pest control measures designed to eliminate these household triggers. The results were unexpected — and clear. Getting rid of pests didn’t lower the frequency of asthma attacks in these children.
This challenges a widely accepted strategy. Many families have invested significant time and money in pest-free cleaning routines, believing it would keep asthma at bay. But according to the evidence, a spotless home doesn’t offer the protective effect people assume.
Other popular health practices experts say don’t work as expected
The household cleaning myth is just one of nearly 400 “medical reversals” uncovered in a comprehensive analysis of more than 3,000 studies published in JAMA, The Lancet, and The New England Journal of Medicine. Here are some of the most surprising examples:
- Peanut exposure and allergies: Pediatricians once recommended keeping children away from peanuts for their first three years. But studies showed that early exposure — even before age one — doesn’t increase allergy risk.
- Fish oil and heart disease: Omega-3 supplements were once believed to prevent heart problems, but a major trial of 12,500 high-risk patients found no protective effect.
- “Baby simulator” dolls and teen pregnancy: Giving teenage girls lifelike dolls was supposed to deter early pregnancies. Instead, girls who participated were slightly more likely to become pregnant than those who didn’t.
- Ginkgo biloba and memory: Once promoted for brain health, the supplement was proven ineffective in a large federal study — yet it still generates hundreds of millions of dollars in sales annually.
- Fitness trackers for weight loss: Surprisingly, dieters who used step counters and calorie trackers lost less weight over two years than those following standard advice without gadgets.
- Surgery vs. physical therapy for torn meniscus: Patients with moderate arthritis who tried physical therapy improved just as much as those who underwent surgery.
These findings show how medical knowledge evolves. Health advice, even when widespread and well-intentioned, isn’t always correct. That’s why questioning long-held assumptions and staying informed matters more than ever.