Inclusion Criteria Healthy Volunteers (only included in part A of the study):  Aged 18 years or older Sufficient knowledge of the Dutch language  Exclusion Criteria Healthy Volunteers (only included in part A of the study):  Subjective presence of nasal disease (i.e. the study subject indicates to experience any nasal symptoms, an occasional common cold not taken into account) Established diagnosis of a nasal disorder (e.g. allergy, nasal polyps, …) or a positive allergy test (skin prick test or blood test) Prior nasal surgery Asthma Use of an oral corticosteroid in the month prior to the screening visit Significant disease(s) that might interfere with the study, based on the judgement of the investigator Current use of a nasal decongestant, more than two episodes of 7 days use of a nasal decongestant in the previous year or less than two episodes of 7 days use (in the previous year) but last use less than a month prior to the screening visit Other medication used to treat nasal symptoms (intranasal corticosteroids, oral or intranasal antihistamines, oral decongestants …) History of rhinitis medicamentosa (either patient-reported long-term use of a nasal decongestant or a diagnosis of rhinitis medicamentosa) Pregnancy, trying to become pregnant (during the duration of the study) or breastfeeding  Inclusion Criteria patients with long-term use of nasal decongestants: part A:  Aged 18 years or older Daily use of a nasal decongestant for at least 6 months. Following ATC-codes are considered, when the spray or drops contain a nasal decongestant and the drug is thus intended for short-term use only: R01AA, R01AB, R01AD52, R01AD53 Sufficient knowledge of the Dutch language  Exclusion Criteria patients with long-term use of nasal decongestants: part A:  Pregnancy, trying to become pregnant (during the duration of the study) or breastfeeding Use of an oral corticosteroid in the month prior to the screening visit Use of an oral decongestant in the week prior to the screening visit Significant disease(s) that might interfere with the study, based on the judgement of the investigator  Inclusion Criteria patients with long-term use of nasal decongestants: part B:  Aged 18 years or older Daily use of a nasal decongestant for at least 6 months.Following ATC-codes are considered, when the spray or drops contain a nasal decongestant and the drug is thus intended for short-term use only: R01AA, R01AB, R01AD52, R01AD53 Sufficient knowledge of the Dutch language  Exclusion Criteria patients with long-term use of nasal decongestants: part B:  Pregnancy, trying to become pregnant (during the duration of the study) or breastfeeding Glaucoma Use of an oral corticosteroid in the month prior to the start of the intervention Use of an oral decongestant in the week prior to the start of the intervention Significant disease(s) that might interfere with the study, based on the judgement of the investigator