Carbon nanotubes (CNTs) find their extensive application as a promising material in medicine due to unique characteristics.
However, such materials have been accompanied with potentially hazardous effects on human health. The toxicity of CNTs may vary depending
on their structural characteristics, surface properties and chemical composition. To gain insight into the toxicity of CNTs in vivo
and in vitro, we summarize contributing factors for the toxic effects of CNTs in this review. In addition, we elaborate on the toxic effects
and mechanisms in target sites at systemic, organic, cellular, and biomacromolecule levels. Various issues are reported to be effected
when exposed to CNTs including (1) blood circulation, (2) lymph circulation, (3) lung, (4) heart, (5) kidney, (6) spleen, (7) bone marrow,
and (8) blood brain barrier. Though there have been published reports on the toxic effects of CNTs to date, more studies will still be
needed to gain full understanding of their potential toxicity and underlying mechanisms.