Abbreviations
APC: antigen-presenting cell
AUC: area under the curve
BCC: basal cell carcinoma
cAMP: 3′,5′-cyclic adenosine monophosphate (cyclic AMP)
CBC: complete blood cell count
CCR4: C-C chemokine receptor 4
CTCL: cutaneous T-cell lymphoma
CTLA4: cytotoxic T lymphocyte–associated protein 4
DEET: diethyltoluamide (N,N-diethyl-m-toluamide)
DHT: dihydrotestosterone
ECP: extracorporeal photopheresis
En1: engrailed-1
EMA: European Medicines Agency
FDA: U.S. Food and Drug Administration
5FU: 5-fluorouracil
GI: gastrointestinal
GM-CSF: granulocyte-macrophage colony-stimulating factor
G6PD: glucose-6-phosphate dehydrogenase
GRASE: generally recognized as safe and effective
HPV: human papillomavirus
HSV: herpes simplex virus
IFN: interferon
IL: interleukin
IVIG: intravenous immunoglobulin
JAK: Janus kinase
MRGPR: Mas-related G protein-coupled receptor
MRSA: methicillin-resistant Staphylococcus aureus
mTOR: mammalian (or mechanistic) target of rapamycin
NSAID: nonsteroidal anti-inflammatory drug
ODC: ornithine decarboxylase
OTC: over the counter
PABA: p-aminobenzoic acid
PD-1: programmed death-1
PDE: cyclic nucleotide phosphodiesterase
PDT: photodynamic therapy
PUVA: psoralen and UVA
RAR: retinoic acid receptor
REMS: risk evaluation and mitigation strategy
RXR: retinoid X receptor
S1PR1: sphingosine-1-phosphate receptor 1
SPF: sun protection factor
SSD: silver sulfadiazine
SSTI: skin and soft-tissue infection
STAT: signal transducer and activator of transcription
TNFα: tumor necrosis factor α
TPMT: thiopurine S-methyltransferase
TRPV1: transient receptor potential vanilloid type 1
TYK2: tyrosine kinase 2
UV: ultraviolet
VZV: varicella-zoster virus
The skin is a biologically active, multifunctional, and multicompartment organ. Medications can be applied to the skin for two purposes: to directly treat disorders of the skin and to deliver drugs to other tissues. Effective and safe use of topical pharmacological therapies requires an understanding of skin physiology and factors influencing percutaneous drug absorption and metabolism (Hwa et al., 2011; Wolff et al., 2008). General features of skin structure and percutaneous absorption pathways are outlined in Figure 75–1.