Based on its large-scale, ubiquitous sensing ability of the physical world and its direct interaction with users, Mobile Crowd Sensing can be used for public health monitoring and improvement of the quality of life of patients. This paper presents Allergymap, a mHealth mobile crowdsensing system that aims to address several aspects of management of allergic diseases, like identification of allergens season onsets, patient stratification, control of allergy and monitoring treatment progress. Subjective data inputs from users, as well as objective environmental data from fixed stations, are inserted into the system (in a privacy-aware manner) for further processing and analysis, and finally exporting data visualization in distinct spatial maps The envisioned system attempts in a novel way to combine a hybrid architecture for analysis and visualization of allergens and irritants onsets, as well as new methods for increasing patient's stratification to treatment. Also, some additional features are implemented for motivating users to become members of Allergymap community and enhance its potential. The system is currently deployed and validated in a multidisciplinary case study for Greece but is general enough to be used in any region.