The possibility of health effects related to nanoparticles (less than 100 nanometers diameter) exposure may be considered as an emerging problem. Current approaches are usually partial and do not consider the multidisciplinary available data. The purpose of this work is to define the problem using an evidence-based approach: we characterized the possible nanoparticles-human interactions by collection of all pertinent scientific data available in the literature and by their critical evaluation. The distinction between non-intentional nanoparticles ("ultrafine particles", UFP) and intentional nanoparticles ("intentionally produced nanomaterials" or simply "nanomaterials", IPN) is a critical item. Each single type of nanoparticle is more relevant than isolated metric characteristics. Globally, the experimental studies suggest a possible inflammatory acute effect. The available data regard mainly the UFP. Regarding IPN, the studies about attaints on human health are actually few and limited: no cardiovascular. respiratory and coagulation effect were showed as consistent with exposure. No human study about IPN chronic effect is available, and any human data is not showed relating carcinogenic and sensitizing effects.