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18Monitoring the levels of trace elements in hair can allow estimating the effects of the geographical 19 location and also can provide a notion of the metal body burden. However, the use of human hair is 20 controversial due to different confounding factors that could affect the presence of trace elements 21 in hair. As a result, a comprehensive monitoring study was performed in Alcalá de Henares, one of 22 the major cities in the Madrid Region, Spain. Trace elements have been monitored in urban topsoils 23 and in human hair of two well-defined and healthy groups of population: children (6-9 years) and 24 2 adolescents (13-16 years). The city was divided into four areas or zones with different characteristics 25 to assess the possible effect of the area of residence and the age in the presence of Al, As, Be, Cd, Cr, 26Cu, Hg, Mn, Pb, Sn, Ti, Tl and Zn in soils and hair. There is no current hypothesis that explains the 27 possible effect of the area of monitoring in the distribution of Be, Cr, Ni, Sn and Ti found in these 28 urban soils, maybe because urban soils receive high disturbance and there are many factors 29 involved. The presence of most of the trace elements monitored was significantly higher in the hair 30 of the children population, except for Sn and Zn. This could be attributed mainly to dietary habits. 31Other factors influencing metal content in hair such as environmental factors would have had a 32 minimal effect in the population groups here studied. Finally, none of the levels of trace elements 33 studied in hair were significantly correlated with levels measured in the topsoils of public parks in 34Alcalá