We introduce a new optical method to noninvasively and continuously measure the swelling process of the nasal mucosa whereby we use light of different wavelengths in the red and near-infrared range which is transilluminated through the nasal tissue and whose extinction is recorded as a function of time. From the temporal and spectral extinction data, we are able to extract characteristic parameters that describe the swelling process quantitatively by means of a regression-type parameter estimation algorithm. The method has been applied to the nasal allergen provocation test and verified on a limited number of volunteers.