Abstract: A method, a communication system and a computer program for providing information indicative of concentration of allergens in the environment. A person detecting a respiratory difficulty symptom (presumably due to the presence of an allergen in the environment) records information relating to the detected symptom using her/his mobile device. The recording comprises providing subjective information relating to the detected respiratory difficulty symptom via a graphical interface of the mobile device. The mobile device completes the information relating to the detected symptom with automatically generated objective information (date and time). Then, at least part of the recorded information relating to the detected symptom is shared by the mobile device on a sharing server. Any other mobile device may receive the share part of the recorded information relating to the detected symptom from the sharing server and display it on a map shown by its display.