While many clients tolerate electrolysis without requiring pain relief, it's overpromise to state that treatment will be painless for all consumers.
- "100% permanent"
The vast majority of patients experience permanent removal of treated hair over the course of treatment, but published studies have observed that between 7% and 10% of consumers did not have satisfactory results.
- "Guaranteed 0% regrowth"
There is no published clinical data to substantiate this sort of overpromise.
- "Easy to use" personal units
Small battery-powered probe units like the One Touch may claim to be easy to use, but performing electrolysis on yourself is very difficult and not recommended. [2, 3]
Three kinds of energy are used:
Galvanic electrolysis works by causing salt and water in the skin around the probe to be chemically altered to produce a small amount of sodium hydroxide, or lye. Lye is the active ingredient in some crystal drain openers. If enough is produced, it can damage the cells that cause hair growth. The chemical reaction is expressed like this:
NaCl (salt) + H2O (water) + direct current = NaOH (sodium hydroxide) + Cl (chlorine) + H (hydrogen)
Thermolysis works by causing water molecules in the skin around the probe to vibrate, which creates heat. If enough heat is produced, it can damage the cells that cause hair growth.
Blend is based on the theory that lye is more caustic when heated. Theoretically, blend is more effective if performed correctly. Blend is recommended by several experts, [4, 5, 6] but electrologist skill is by far the most important factor in safe and effective treatment.
Although several researchers were apparently experimenting with electrical epilation after the Civil War, it's generally accepted that St. Louis ophthalmologist Charles Michel was the first to discover and publish permanent hair removal results with an electrified needle. 
In 1875, Dr. Michel reported he had been successfully using a battery-powered needle epilator to treat ingrown eyelashes (trichiasis) since 1869.  This DC powered method was called electrolysis because a chemical reaction in the hair follicle causes sodium hydroxide to form, which damages the follicle. It's also sometimes called galvanic electrolysis.
Use of electrolysis for hair removal continued through the early part of the 20th century. Its commercial popularity as a cosmetic treatment was briefly eclipsed by x-ray hair removal, which was advertised as both "painless" and "harmless" (only one of which was true, of course).
Subsequent innovations in the field included the use of multiple needles, developed by Paul Kree in 1916, and the use of AC electricity, which causes thermal damage within the follicle.  This was first reported in medical literature in 1924 by Dr. Henri Bordier, following over a decade of experimentation by numerous researchers.  This method was called diathermy by Bordier and is also called thermolysis, short-wave, high-frequency (HF), radio-frequency (RF), etc.
Incremental improvements in the equipment and technique continued through World War II. At that time, Arthur Hinkel and Henri St. Pierre applied for a patent for a blend method they'd been developing. They received their patent in 1948, and 20 years later published the groundbreaking book Electrolysis, Thermolysis and the Blend, discussing their use of scientific techniques to improve the method.  In the wake of Hinkel's book, several other useful practical overviews have been written. [4, 5, 6]
The second half of the 20th century saw more incremental equipment improvements incorporating transistors and computerized controls, as well as insulated probes and sterile disposable probes.
Despite improvements in equipment, electrolysis remains highly dependent on the skill of the practitioner. Electrolysis trade groups have set standards for member certification, but many U.S. states do not regulate the practice of electrolysis.  For this reason, it's very important for consumers to go to a practitioner recommended by someone who is done and happy with the results.
Following a long absence from medical literature, electrolysis was once again taken up as an issue worthy of research in the latter part of the 20th century. [13, 14]. Good review articles by physicians [15, 16] complement the practice manuals by professional electrologists. [4, 6, 11]. The best electrolysis book written and edited by a physician is Richards. 
Electrolysis improperly performed or performed on non-normal skin can cause scarring,  spread infection,  and potentially cause isomorphic outbreaks or spread of lesions. 
One well-designed study found that about 2% of women under 50 who seek electrolysis have an undiagnosed glucose intolerance. 
Two studies, one small and one large, respectively demonstrated that 90% to 93% of consumers have satisfactory results [21, 22]
Two well-designed Japanese studies demonstrate permanence in treating underamrs. The thermolysis study showed "little to no regrowth" at 6 to 36 months after 3 to 8 treatments to the underarm.  The blend study observed no regrowth at 6 months after 7 to 14 treatments, while comparative plucking resulted in no significant hair removal at 6 months.