Caffeine skin patches, akin to nicotine patches, have been on the market for a little while, and feedback I found so far is benign. Yu and Soni also promise that the absorption through the skin into the blood will be more gradual, leading to lower highs and higher lows than most stimulant products. That does line up with research on caffeine skin patches that says transdermal caffeine can work, though less efficiently than lower doses taken by mouth. Of course if you take enough, expect to crest and crash in the same way you might with any other caffeine product. (via The New Coffee Is Made for Your Skin – James Hamblin – The Atlantic)