Mixing a stimulant chemical like caffeine with something meant to be worn already sounds like a pretty bizarre idea. But in addition to the concerns of whether or not such a thing is even possible, there is the question of proper warnings and cautions on packaging.
TIME reports on an offering from Hammacher Schlemmer, a clothing company that now offers a "caffeine infused slimming tank top." The product's description claims that it contains "micronized caffeine" which can be absorbed through the wearer's skin and lead to a reduction in fat for the wearer.
The author of the TIME piece, Doug Aamoth, is rightly skeptical of such a claim, especially where the description instructs the wearer to keep it on for 21 days to feel the full effect.
In between eyerolls, this does raise an interesting question: should clothes that follow in this trend take a cue from coffee labels in the way they handle caffeine content? Just because a potentially dangerous ingredient is a little more dormant in a certain product may not mean there isn't cause to be concerned. This can be a particular concern given the large amount of caffeine exposure many are seeing, as the Daily Mirror notes.
Printing prime labels in advance and with full knowledge of what consumers and companies are looking out for is an aspect of your business that can lead to more success. Labels for consumer products can come under special scrutiny when they contain an ingredient like caffeine, and if "contact stimulation" from this chemical is possible, then you will need to recognize that.