My House Is Giving Me a Mucus Cough and I Can’t Figure Out Why

Hi everyone - I’m hoping someone here has experienced something similar or can point me in the right direction, because I’m officially stumped. For the past few months, I’ve been waking up every single morning with a mucus cough. It hangs around most of the day and then weirdly eases off by the evening. It’s at its worst in the morning, especially the first 2–3 hours after I wake up, and it comes up a bit more after I eat too. It’s becoming really disruptive at work. My voice keeps breaking and I’m constantly clearing my throat, which is mortifying in a quiet office lol. I don’t want people thinking I’m sick and came into work when I’m actually fine — it’s just this persistent mucus in my throat that i'm coughing up. At first, I thought it had to be food-related because it seemed to kick in after breakfast. I tried changing my diet — I don’t consume dairy anyway, but I also tried going low sugar. I even skipped breakfast altogether, tried supplements even fasting. No change. Still coughing up mucus. Next theory: allergies. I do have a slight dust allergy, so we went all in. Daily hoovering, a proper HEPA air purifier in the bedroom (which I move to the living room when I work from home), and anti–dust mite spray on the mattress and sofa. We don’t have carpets, so it’s not especially dusty — but still no improvement. This all started around May 2025 (we moved into our new home in April) and it’s been progressively getting worse — more mucus, and lasting longer throughout the day. We also wondered about mould. I’m a pretty good cleaner, we use a dehumidifier when drying clothes indoors, and we keep the house well ventilated (need to keep the UK dampness at bay). There’s no visible mould anywhere, and my husband is completely fine. The reason I keep coming back to the house is that whenever we go on holiday, the mucus cough completely disappears. Even when I stay with my parents for a week at theirs nearby — where the air quality is probably the same — it goes away. I’ve spoken to my GP and she’s just as confused. She suggested trying fexofenadine for two weeks, which didn’t help. She mentioned a chest X-ray but said it’s unlikely to show anything. At this point I’m wondering if I’m missing something obvious. Are there any doctors here who could offer some insight, or anyone who’s dealt with something similar? I’d really appreciate any thoughts.