The Short Version
Customs officers should avoid smell-testing unknown powders and should handle them only with proper protective procedures. But the claim misstates why: fentanyl is highly potent, yet the evidence does not show that brief skin contact is likely to be lethal, and “microdoses” is not an accurate description of the commonly cited potentially fatal amount. The real concern is aerosolization, inhalation, or mucous-membrane exposure when powder is disturbed.