A 14-year-old boy who complained of a chronic rash on his left arm and hand has been diagnosed with a “tefillin rash” – caused by the chemical potassium dichromate, which is used to process the black straps of the phylacteries.

An article in the September issue of the Hebrew-language medical journal Harefuah (of the Israel Medical Association) by doctors at Sha’are Zedek Medical Center describes the unusual case.

The boy was described as the youngest person to be recorded with such an allergic reaction to leather tefillin straps. Other victims have been as old as 77 (such a man was diagnosed after 20 years of suffering from allergic contact dermatitis).

Others were devout men, including rabbis, who wear their phylacteries not only to recite the morning prayers but also keep them on all day as an “extra mitzva.”

“Tefillin allergy” is relatively rare in Israel. It is due not to the tefillin themselves, but to the chemicals used to process the leather straps. Almost all cases involve the phylacteries worn on the arm, but there are rarer cases in which those worn around the head and touching the neck also cause rashes there.

The rash appeared in the boy about a year after he first began to don phylacteries for his bar mitzva, wrote Drs. Pinhas Hashkes and Efraim Sagi of the Jerusalem hospital.