Living in LA, a place known for its air pollution, means that you will be surrounded by more allergy/asthma/lung condition sufferers. Thus this is likely the cause of the things you have observed. Alternatively you may consider that a perfume/lotion/detergent (or other scent not produced by you) is too strong for many people. If your sense of smell is hyposensitive (instead of hypersensitive), then you might not notice how strong certain scents are to others.