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Skin Deep is a blog for dermatologists and skin care professionals with focus on theoretical, cosmetic and aesthetic dermatology. This blog is associated with ‘Dermatologists Sans Borders’ one of the largest curated groups of skin care professionals on facebook. If you are looking for non-technical information, please visit

The Naranjo algorithm

English: A hand scratching at a pruritus on arm
A hand scratching at a pruritus on arm (Photo credit: Wikipedia)
For decades, retinoic acid (RA) is known as the most potent therapeutic option in the therapy of acne. A recent study (1) suggests inhibition of endogenous RA metabolism and amplification of endogenous RA signalling as a mechanism underlying the biochemical actions of antibiotics such as tetracycline and erythromycin in acne therapy. So, at the fundamental molecular level, the mechanism of action of these disparate agents converge.

The mechanism of pruritus in Dandruff/seborrhoeic dermatitis (D/SD) is not well understood. Histamine is one of the biomarkers of pruritus now widely used in treatment efficacy trials. The exact mechanism leading to histamine release and pruritus is not yet clear. This study (2) demonstrated significant increase in cathepsin S in D/SD and recommends it as a potential marker of pruritus in D/SD and in assessing the effect of anti-dandruff treatments.

Recently I came across The Naranjo algorithm, Naranjo Scale, or Naranjo Nomogram, a questionnaire designed by Naranjo et al. for determining the likelihood of whether an ADR (adverse drug reaction) is actually due to the drug rather than the result of other factors (3). Probability is assigned via a score termed definite, probable, possible or doubtful. Dermatologists are usually consulted whenever there is a suspected ADR, but I never knew about this methodology till now.

Itching (Photo credit: amareta kelly)

1. Hellmann-Regen, J., Herzog, I., Fischer, N., Heuser, I. and Regen, F. (2014), Do tetracyclines and erythromycin exert anti-acne effects by inhibition of P450-mediated degradation of retinoic acid?. Experimental Dermatology, 23: 290–293. doi: 10.1111/exd.12358

2. Viodé, C., Lejeune, O., Turlier, V., Rouquier, A., Casas, C., Mengeaud, V., Redoulès, D. and Schmitt, A.-M. (2014), Cathepsin S, a new pruritus biomarker in clinical dandruff/seborrhoeic dermatitis evaluation. Experimental Dermatology, 23: 274–275. doi: 10.1111/exd.12357


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About Me

As a Dermatologist and Informatician my research mainly involves application of bioinformatics techniques and tools in dermatological conditions. However my research interests are varied and I have publications in areas ranging from artificial intelligence, sequence analysis, systems biology, ontology development, microarray analysis, immunology, computational biology and clinical dermatology. I am also interested in eHealth, Health Informatics and Health Policy.


Bell Raj Eapen
Hamilton, ON