And those figures do not account for wages lost while training, or tuition for required schooling, which can be steep -- as much as $18,000 for cosmetology school in Utah. That's a lot of time, money, and effort spent earning a license instead of a living.

The dirty little secret of licensing is that no one likes it more than the licensed. Rarely, if ever, do consumers clamor for protection from unlicensed providers, nor should they. Licensing costs consumers billions a year in higher prices and does little to improve service quality.

Instead, licensing typically results from industry interests lobbying for laws to limit competition. And once those laws are in place, established interests will use them aggressively to target unlicensed competitors.

A 2011 strategy document for the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) identified a "significant competitive threat" to registered dieticians from nutrition professionals, nurses, pharmacists, and others providing nutritional advice and urged dieticians to "increase our vigilance in reporting unlicensed competition" to state authorities. Interior designers have done the same: 95 percent of complaints to interior design regulatory boards were licensure-related, one study found, while just 1.6 percent were for fraud or other genuine consumer complaints.

Licensing vests enormous power in such regulatory boards, usually filled by law with members of the licensed occupation. Boards have tremendous incentives to curb competition, particularly innovative techniques or business models, and to expand their reach.

Thus, Western-style cosmetologists claim dominion over increasingly popular services like African-style hairbraiding, South Asian and Middle Eastern eyebrow threading, and Asian fish pedicures, even though cosmetology schools rarely teach such practices. And dental boards in North Carolina, Connecticut, and elsewhere demand that entrepreneurs providing over-the-counter teeth-whitening products become licensed dentists.

The result of all of this special-interest politicking is a tangle of licensing laws that makes little sense. For example, it seems reasonable that most states require about a month of training to become an emergency medical technician, an occupation with clear health-and-safety implications. But it is implausible that barbers and cosmetologists need 10 times as much training as EMTs, as most states require.

Imagine the effect on employment if more occupations were freed from barriers erected to protect special interests from honest competition

Similarly, manicurists need only about three days of training in Alaska and nine in Iowa. Surely the 10 states that require four months or more could get by with less. Only five states license shampooers. Is there an epidemic of dangerous shampooing everywhere else?