UV tattoos, also known as blacklight tattoos are created and made with a special 'invisible ink that remains almost unseen. Much more visible at a closer range of the tattoo. They omit a really cool neon glow under ultraviolet light, or a black light. Depending on the specifics of the ink itself, they can be more or less subtle in lighting environments that don't have UV light. Although a good choice for someone with a more subtle tattoo idea in mind, they are a hot choice for your typical raver who indulges in that culture.
The tattoos are technically invisible in normal lighting, giving off a slight outline depending on the ink used and what/where the tattoo is. The colors it can glow ranging anywhere from a bright white, purples, greens, and so forth. Special colored ink is also available for these occasions. They look like completely normal tattoos in your average lighting. However, in a blacklight they do just what regular UV tattoos do: Glow!
Funny enough with tattoo ink, is that the FDA(Food and Drug Administration) does not and has not regulated tattoo ink(s) or the pigments in it used. Any claims made that have said UV tattoo ink is FDA Approved in any shop, or anytime being used is complete fraudulence. There's been UV-reactive inks that can possibly have been approved by the FDA if the ink had some important food relation. UV Tattoo ink is far more expensive and harder on your wallet then just the generic and typical ink used. There's been some recorded cases of people having reactions to the ingredients in the ink itself, but nothing major. Small symptoms, such as: minor itching, irritation, and dermatitis. There are UV inks that are suspected of containing specific carcinogens and allergens. Unfortunately, there hasn't been enough studying and research done on this to truly reveal the long lasting effects of exposure.
There are some who have actual physical reactions to the ink when being tattooed, but is not really ink specific as normal ink can cause the user to have the same reactions. Oddly enough, this could be a result of using lotions, and any other sort of scented creams and the likes on the area that was tattooed. Not protecting it from UV light for the first 3 months has been speculated as a probable addition to the physical reactions.
If the above listed is your case, this can actually damage the ink on your tattoo. Sometimes causing it to become a regular color of ink at all times. Overtime it also may not shine as much, or at all under blacklighting. Blue and Clear inks specifically are noted for their turning of color over time. From a yellow, or turning to a slight brown from over sun exposure. Colored and black UV inks are more notable for becoming colored all the time in general, taking upon the appearance of a normal tattoo.
In the more recent years, UV inks have drastically improved in their formula used. It's definitely becoming more of an occurrence to have UV tattoo success stories with little to no reactions at all. They can also be very suitable for someone who may or may not be able to place tattoos on certain parts of their body due to their employment, or other life reasons. This is of course until the person becomes under a blacklight/UV light.
UV ink itself varies differently from regular ink. It for certainly isn't as bright as normal ink is, and does not blend like regular ink. If using normal ink on top of the UV ink, the effects will be trivial. This is also why tattoos that have a much bigger visual impact in color and vibrancy are done in regular ink first. Then, the tattoo is given time to heal over before being artistically highlighted with UV ink. Proficient and highly skilled tattoo artist are usually more applicable to apply the ink as well as a large enough light to see the tattoo as it's being drawn and applied.
UV inking itself takes more time to apply due to it being much harder to work with due to it having a thinner consistency, and lastly needing the tattoo to be wiped and checked often during the session.