The published results of breath isoprene studies, to date largely involving adults, are briefly reviewed with special attention given to the work done on this topic during the last 10 years using selected ion flow tube mass spectrometry, SIFT-MS. Then the new data recently obtained on isoprene levels in the exhaled breath of some 200 healthy children and young adults (pupils) with ages ranging from 7 to 18 years measured using SIFT-MS are presented in detail. A concentration distribution has been constructed from the data obtained and compared to that for healthy adults also obtained from SIFT-MS data. Although there is overlap between the two distributions, which are close to log normal in both cases, the median level for the young cohort is much lower at 37 parts-per-billion, pbb, geometric standard deviation, GSD, 2.5, compared to that for the adult cohort of 106 ppb with a GSD of 1.65. Further to this, there is a clear increase in the mean breath isoprene concentration with age for the young cohort with a doubling of the level about every 5-6 years until it reaches the age-invariant mean level of that for adult cohort. Should this trend be extrapolated downwards in age it would indicate a near-zero breath isoprene in the newborn that was indicated by a previous study. Indeed, in the present study isoprene was not detected on the breath of two young children. The results reveal mean breath isoprene levels (±SD) for pupils within the given age ranges as 7-10 years (28 ± 24 ppb), 10-13 years (40 ± 21 ppb), 13-16 years (60 ± 41 ppb) and 16-19 years (54 ± 31 ppb). The more rapid increase that occurs between the second and third age ranges is statistically highly significant (p = 0.001) and we attribute this phenomenon to the onset of puberty and the spurt in growth that occurs during this phase of development. There is no significant difference in mean breath isoprene between males and females for both the adult cohort and the younger cohort.