A “too clean” lifestyle is usually discussed through the hygiene hypothesis, the idea that reduced early-life exposure to microbes is linked with higher allergy risk. The modern version is more nuanced: it does not argue that dirt is always good, but that some everyday microbial contact—especially early in life—may help train immune regulation.

A historical review of the hygiene hypothesis describes how lower hay fever rates in larger families and farm-raised children helped shape this idea, with farming exposure sometimes linked to much lower hay fever prevalence. At the same time, the same review is clear that the exact biological mechanism remains uncertain, despite decades of research, meaning “cleaning causes allergies” is too simplistic.

Where the evidence becomes more concrete is the chemical side of cleanliness. In a Canadian birth cohort, more frequent household cleaning-product use in infancy was associated with higher odds of recurrent wheeze and asthma diagnosis by age three. This pattern fits a straightforward explanation: many cleaning products release irritants or reactive compounds that can inflame sensitive airways, especially in babies who spend most time indoors and breathe more air per body size. In this picture, the risk is not that cleaning “prevents immunity,” but that over-cleaning can increase respiratory stress and symptoms in vulnerable households.

Air filtration is a second place where “more” can be both helpful and misguided. A large systematic review and meta-analysis of real-world portable air-cleaner studies found average reductions of about 49% for PM2.5 and 44% for PM10, and it also reported meaningful decreases in airborne biological pollutants in some settings. That supports air cleaning as a practical tool during wildfire smoke, heavy traffic exposure, or for people sensitive to dust and pollen.

The catch is that most devices showed little effect on gaseous pollutants, and real-world effectiveness often drops because people run units on low settings or for limited hours due to noise, drafts, and electricity cost. Some air-cleaning technologies can also produce by-products, so “stronger” is not automatically “safer.”

The most science-aligned approach is targeted control: filter when there is a particulate problem, disinfect when infection risk is present, and otherwise prioritize regular cleaning with lower-irritant products and good ventilation. Hygiene can prevent illness, but a home that constantly smells of disinfectant and/or is 'too clean' may be solving one risk while quietly creating another.