Secondhand, or "secondary," asbestos exposure happens when an asbestos professional, construction worker, farmer or someone else who is consistently around the flame-resistant mineral unknowingly brings asbestos fibers home. This inevitably puts everyone in that home at risk for asbestos related health complications.
Asbestos is a mineral found in rock and soil that had been used for years in building and home insulation because of its flame-resistant properties. Since its widespread use in the 20th century, researchers have found a link between asbestos and quite a few illnesses including mesothelioma and lung cancer. For this reason, many countries around the world have either limited or completely banned its use in construction.
But since asbestos was used so frequently in construction prior to these scientific findings, people who work in fields that require demolition or construction of 20th century homes and buildings are at higher risk of developing asbestos-related illnesses.
Airborne fibers from asbestos can stick to clothing, putting family members close to these workers in harm's way. In a study of over 90 women with mesothelioma, the most well-known cancer associated with asbestos exposure, 64% had experienced secondary exposure. Their exposure was non-occupational and not related to anything they'd come in direct contact with.
Unfortunately, since mesothelioma in children and young people is so rare, there's not as much research on the subject as there is for other illnesses. In the rare case that children or young adults experience illness due to asbestos exposure, their exposure is usually secondhand as well. Mesothelioma usually takes 10 to 40 years to manifest, which is why rates of the rare cancer are higher among older people. In leiu of possible environmental asbestos exposure, children and young adults who have mesothelioma or other asbestos-related illnesses likely received it from fibers brought into their home by someone who works in a field where they come in contact with asbestos often.