The big doubt about tattooing comes down to picking a design that you can live with forever. Many people are curious about trying something temporary but are confused just as to how that can be done and and how long the process can be made to last. The difference between permanence and trial is depth of application, the contrast between in the skin and on the skin. The usage of the phrase “temporary tattoo” or "henna tattoo" for processes like henna body painting have further confused people as to what is happening and for how long.

Tattooing

A tattoo is ink that has been pushed down into the middle layers of the skin. What makes it stay is the placement, about one eighth of an inch down, at just the right depth. Too deep and the body will absorb and remove the ink, leaving an uneven or pale design. Tattoo too shallowly and
the design will “heal out” and be carried away when the surface scab drops off the tattoo.

The skin is the largest organ of the body and the outer layer sheds every couple of days. It is so slow and subtle you usually don't notice as regular bathing removes this layer. Sometimes you may notice a tiny area peeling a bit when you dry yourself off after the shower and that's about it. Getting a major sunburn and peeling then is the extreme demonstration of this procedure and most of us who feel and see that don't want to repeat it.

Stick-on Tattoos

Temporary tattoos are a thin plastic or dye that sticks to the surface of your arm or torso or ankle. They will last for several days before slowly peeling off. They usually can be washed off with an oil or rubbing alcohol depending on what they are made of. They can be made to last longer by not letting water run right on them when you bathe and by patting them dry gently, NOT rubbing which will scrape the design off. When they do tattoos in movies, they repaint everybody daily to maintain the look using alcohol based paint/makeup that won't come off in water or with sweat.

Henna

Henna body painting can last for several weeks. It is a plant that is ground up to make a paste with other herbs and usually eucalyptus oil and either tea or coffee to make it darker. The resulting greenish paste is painted on the skin and coated with a lemon sugar glaze to keep the endothermic reaction going longer. It leaves an orange or reddish or brown stain, which will vary with individual response, recipe and length of application. It stains down deeper than just the surface, but once again, as the skin replenishes itself, the stain gradually fades. It will leave the darkest stain on the palms of the hands and fingertips, along with the soles of the feet. The designs will also fade from these areas the fastest as the skin refreshes the fastest on surfaces with the most contact. Designs can last from days to weeks and vary widely.

If you're looking for more information on how to tattoo, you might like
Tattooing A to Z: A Guide to Successful Tattooing
by Huck Spaulding
Advanced Tattoo Art (How-to Secrets from the Masters)
by Doug Mitchel