Nasal congestion from a cold often feels worse indoors than outdoors, with several factors contributing to this phenomenon. One theory suggests that cold air, being denser, allows for a higher concentration of oxygen per breath, making it easier to breathe outside. In contrast, indoor air tends to be warmer and can have a higher concentration of allergens and pollutants, such as dust and cooking fumes, which may exacerbate congestion. Additionally, the accumulation of carbon dioxide indoors can lower oxygen levels, further complicating breathing. Physical activity, such as walking outside, can also help open nasal passages, potentially alleviating symptoms. The discussion highlights that this effect can occur across seasons, suggesting that it may not be solely related to seasonal allergies. Overall, the combination of indoor air quality, temperature differences, and physical activity levels plays a significant role in the experience of nasal congestion.