Enrolled participants were supplied with xylometazoline hydrochloride 0.1% nasal spray (Otrivin) within 1 day of completing screening, and confirmed receipt and usability of the product via the study app. Upon product receipt, participants were required to re-confirm their eligibility by reporting nasal congestion (described as ‘plugged nose’ in the WURSS-21) of at least moderate intensity (score 5) and at least one other common cold symptom of at least mild intensity (score 3) as per the WURSS-21 questionnaire (Table 1). Participants started treatment on day 0 of the study protocol, which was expected to align with a very early stage of disease progression and peak symptom stage (Supplemental Table 1). This was considered a key period to start treatment of the common cold with xylometazoline hydrochloride 0.1% to relieve nasal congestion.