RESUMEN
<p><b>OBJECTIVE</b>To investigate the influence of the depth of skin press in blunt tip placebo acupuncture needles on patient blinding and its relationship to needle diameter.</p><p><b>METHODS</b>Forty healthy volunteers were enrolled as subjects for patient blinding. Four acupuncturists applied the following needles randomly at three points in each forearm: 0.18 mm and 0.25 mm diameter penetrating needles inserted to a depth of 5 mm, and 0.18 mm and 0.25 mm diameter skin-touch needles depressing the skin at the acupoint to a depth of 1 mm and 2 mm from the skin surface. The subjects reported their guesses at the nature of needles they received, and rated needle pain and de qi. A blinding index was calculated to define the success of blinding for subjects.</p><p><b>RESULTS</b>The blinding status of subjects for 1 mm press needles of 0.18 mm diameter was "random guess", but "unblinded" for 1 mm press needles of 0.25 mm diameter. For 2 mm press needles of both diameters, the blinding status was "opposite guess" and the blinding status for penetrating needles of both diameters was "unblinded." The percentages of "felt pain" with 2 mm press needles of both diameters were similar to that with penetrating needles, but those were not similar for 1 mm press needles. The frequency of de qi occurrence with 2 mm press needles of 0.18 mm diameter was similar to that of penetrating needles of both diameters.</p><p><b>CONCLUSION</b>Placebo needles of 2 mm press made more subjects guess that the needles penetrated the skin than 1 mm press needles. The use of small diameter needles increased patient blinding.</p>