Intracellular carrier for long-chain fatty acids and related active lipids, such as endocannabinoids, that regulate the metabolism and actions of the ligands they bind. In addition to the cytosolic transport, selectively delivers specific fatty acids from the cytosol to the nucleus, wherein they activate nuclear receptors (PubMed:21395585, PubMed:22170058). Delivers retinoic acid to the nuclear receptor peroxisome proliferator-activated receptor delta; which promotes proliferation and survival. May also serve as a synaptic carrier of endocannabinoid at central synapses and thus controls retrograde endocannabinoid signaling. Modulates inflammation by regulating PTGES induction via NF-kappa-B activation, and prostaglandin E2 (PGE2) biosynthesis during inflammation (By similarity). May be involved in keratinocyte differentiation (PubMed:8092987). {ECO:0000250|UniProtKB:Q05816, ECO:0000269|PubMed:21395585, ECO:0000269|PubMed:22170058, ECO:0000269|PubMed:8092987}. This is the function of FABP5 (fatty acid binding protein 5, Ensembl gene identifier ENSG00000164687).