THE ANSWER
All three are electrolysis and all three destroy the follicle. They differ in how. Galvanic uses a chemical reaction and is slower per hair. Thermolysis uses heat and is faster. Blend combines them. Which suits you depends on your hair, the area and your skin, and it is a practitioner judgement rather than a ranking.
Why
Galvanic is the original method. A direct current causes a chemical reaction in the moisture of the follicle, producing a compound that destroys the growth cells. It is thorough and it works well on distorted follicles, because the chemical action reaches areas a probe cannot point at directly. It is also slow, taking considerably longer per hair.
Thermolysis uses high-frequency alternating current to produce heat at the probe tip, destroying the growth cells thermally. It is much faster per hair, which makes it practical for dense areas. It depends more on accurate probe placement, because the heat is concentrated where the probe is.
Blend runs both in the same insertion, aiming to combine the thoroughness of galvanic with some of the speed of thermolysis. Many practitioners use it as their default for coarse or distorted hair.
You may also hear flash, micro-flash or pico-flash. These are variations of thermolysis using very short, higher-intensity bursts, generally chosen for speed and comfort on fine hair.
Which method is best for my hair type?
There is no single best. Coarse or distorted hair often suits blend or galvanic; fine hair in dense areas often suits a thermolysis variant. Your practitioner should be able to explain why they are choosing what they are choosing.
What is micro-flash versus pico-flash?
Both are short-duration thermolysis variants, differing in the length and intensity of the pulse. They are generally used for speed and comfort rather than because one is fundamentally superior.
Are the probes disposable?
They should be single use. This is a reasonable and expected question to ask any practitioner before treatment, and a straightforward yes is the only acceptable answer.
What is an insulated probe?
A probe with an insulating coating along its shaft so energy is delivered at the tip rather than along the length. Some practitioners prefer them, particularly for comfort. It is a preference rather than a requirement.
I have a nickel allergy, what probe material should be used?
Raise it before treatment. Probes are available in different materials, including gold-plated options often used for sensitive or allergic clients. Tell your practitioner at consultation rather than after a reaction.
What the evidence says
The three methods are standard and long-established across the field. Method selection is a matter of practitioner judgement based on hair, area and skin, and comparative superiority claims between them are not well supported. This page does not state which equipment or method is used at any particular studio.
What to do next
Ask which method is being used on your area and why. A practitioner who can explain the choice in plain terms is demonstrating something useful about how they work.
If you have a metal allergy, raise it before your first treatment. See how to choose an electrologist and electrolysis consultation.