Our study highlighted an extremely high incidence of unsuspected exposure to drugs of abuse by hair testing in children from a low socioeconomic status cohort in a Mediterranean city [16]. Hair testing for opiates, cocaine, amphetamines, methylendioxyderivatives, cannabinoids and methadone was provided using a highly specific and sensitive screening and confirmation methodology recently developed coupling an immunoassay specific for keratin matrix with last generation ultra-performance liquid chromatography tandem mass spectrometry [14]. In case of parental hair samples, the cut-offs recommended by the Society of Hair Testing were used to discriminate positive samples for both screening and confirmation analyses [15]. Using these cut-offs, no false positive and negative results were found applying screening analysis to adult hair samples, which were always confirmed by chromatographic/mass spectrometric assay. In case of children hair samples, results were considered positive not on the basis of recommended cut-offs—which indeed do not exist for paediatric samples—but when analyte concentration was equal of higher than the confirmatory analysis limit of quantification. The reason was that the international cut-offs for positivity to drugs of abuse were established considering values for adult population of consumers and non consumers of those substances. Conversely, in case of children we considered that none of them could have been assimilated to a consumer (even if accidental intake could not be excluded) since they were younger than 10 years of age, nor intrauterine exposure could have been occurred since they were older than 2 years of age and examined hair strand was of 4 cm, corresponding to the previous 4–5 months. Furthermore, the last generation UPLC-MS/MS allowed a greater sensitivity which permitted to disclose the maximum possible number of children exposed to drugs of abuse, including cannabinoids, whose hair concentration is extremely low even in active consumers [1].

Paediatric hair testing in this study confirmed that children positivity rate to repeated exposure to drugs of abuse matched to parental positivity rate to the same drug in the paediatric sample positive for 6-MAM and morphine, in the single case positive to methadone, in 69.5% cases positive to cocaine and 69.2% cases to cannabinoids, confirming that the first source of paediatric exposure to drugs of abuse are the parents and more in general a risky parental environment. Indeed, in case of children with hair samples positive to drugs of abuse, whose accompanying parent was negative, it cannot be excluded exposure to the other parent or care-giver consumption of drugs or contact with contaminated surroundings. Conversely, the four paediatric cases positive to codeine could have been attributed to the use of antitussive syrups, which in any case was not declared at the visit interview.

The results of the present study are in complete agreement with a previous study of 2009 concerning unsuspected exposure to cocaine in preschool children (younger than 5 years of age) attending the same Emergency Department at Hospital del Mar of Barcelona. That time, we found a 23.3% preschool children (1–5 years of age) positive for cocaine (concentration range 0.3–5.96 ng/mg of hair) with one sample also positive for MDMA and another for opiates. In 88% of the positive cases, cocaine was also found in the hair of the accompanying parent. In that study too, parental sociodemographics were not associated with children’s exposure to cocaine, nor somatometry of children at birth. However, the behavioural patterns with potential harmful effects for the child’s health (e.g., tobacco smoking, cannabis, benzodiazepines and/or antidepressants use, shorter breastfeeding time) were significantly higher in the parents of exposed children [9]. We attributed the high percentage of positive cases to the fact that the preschool children stay at home with a parent or a caregiver the majority of time, but the present study show that this was not the case since high percentages of paediatric exposure was not only found in preschool children, but also in case of 2–11 years old children. It’s noteworthy that in 2009 prevalence of cocaine consumption in the general population was around 3%, while in 2011 it decreased to 2.3%. Nonetheless, this decrease is attributable to all the Spanish population, and not to the specific Barcelona area investigated in our study, where consumption and consequent pediatric exposure has been shown to be higher than the average country data [7,8]. Interestingly, in the same environment, in 2005, we reported a hidden prenatal chronic exposure to cocaine in 4.4% newborns, together with 5.3 and 8.7% exposure to cannabis and opiates, respectively [12]. Taken together, these two outcomes demonstrate the magnitude of the problem of exposure to drugs of abuse among children in this environment.

Concerning exposure to drugs of abuse in paediatric population of this study, it should be said that: firstly external contamination have to be excluded since and extended standardized hair washing was included in the procedure for hair testing. Secondly, as reported by international literature, even if the route(s) of children “passive or active” exposure to drugs of abuse- (e.g., parental consumption in the household, contact with drugs-contaminated surroundings, crawling and putting contaminated objects in the mouth, accidental ingestion), cannot be easily established, contact occurred as proved by positive hair testing with possible risk of subsequent severe intoxications [17,18].

While it has been proved that acute exposure to cocaine during childhood is associated with neurologic manifestations such as focal and generalized seizures in children eight years of age and younger and alterations in mental status, including delirium stupor and coma in older children [19], and even death in cases of oral or inhaled routes of intoxication [8], the long term effects of a repeated postnatal exposure to cocaine have not been clarified yet.

Similarly, whereas children exposure to cannabis was reported to cause developmental delay, hyperactivity, lethargy ataxia, and respiratory insufficiency [20,21], no information on the effects of pediatric chronic exposure to that drug is known.

Nonetheless, even if it is difficult to identify a core set of physical, cognitive, or behavioural problems that can be directly attributed to postnatal (or pre and postnatal) exposure to drugs of abuse, it is well known that paediatric exposure to drugs of abuse is frequently associated with poor child care by the care giver.

In this concern, our previous study showed that parents of cocaine exposed children present, to a significantly higher extent, behavioural patterns with potential harmful effects for the child’s health (e.g., tobacco smoking, cannabis use, benzodiazepines and/or antidepressant use, shorter breastfeeding time). Indeed, a significantly high percentage of those children (11.8%) showed a failure to thrive which would require nutritional assessment and follow-up [9].

The parental risky behaviours are confirmed in the present study: mothers and fathers of children exposed to drugs of abuse smoke more cigarettes and cannabis joints and consume more benzodiazepines and antidepressant drugs.

These confirmed occurrences let us hypothesizes that these children could receive poor familiar attention, in a country like Spain, where drug exposed children are not protected by any specific law promoting foster care or programmed social intervention. Also, consumer parents are not aware of risk of passive environmental exposure in children living in the same environment.