Late 20s is when Bowe starts to see serious candidates for what she calls "prophylactic Botox." The typical case? Fair-skinned individuals who have had a lot of sun exposure growing up.

Other candidates are those who constantly exaggerate facial expressions without realizing it -- the frowners, the squinters, the smilers and the eyebrow-raisers, says Bowe. "By using Botox in a prophylactic way, I actually retrain these muscles to react in a gentler way. I'm still allowing these muscles to move, but not in such an exaggerated way as to lead to etched-in wrinkles," says Bowe.

Diagnosis: Bowe says Emily, 27, is a perfect example of someone with very fair skin, so even a little sun exposure shows fine lines. Emily's forehead lines are horizontal (she's probably one of those "surprised" people) and she has fine lines around the eyes.

Treatment: "Even though her skin looks young and healthy, I would be a little more aggressive to smooth out those lines," says Bowe. "To treat these issues, I can usually get away with using less than 25 units per session, costing the patient $400 to $450. Using such a small amount means that the expression isn't affected -- no frozen faces. I find that I only need to treat these patients twice a year in order to get a very nice result," says Bowe.

Annual Cost: $800-900

Bowe has a self-test for determining who can benefit from Botox in their early 30s: If you find yourself smoothing makeup that collects along a crease or line, you're a good candidate for Botox.

Diagnosis: Bowe says Mary, 31, actually doesn't need to worry about frown or forehead lines. What Bowe does notice is a slight asymmetry. "Her right brow at rest is slightly more sloped downward. When she smiles it pulls down more, almost making the right eye appear smaller. If she doesn't address that early on, the right eye will continue to look smaller and the brows will slope down."

Treatment: "To prevent that, I would lift the eyebrow into an arch. I would put a drop into the outer corner of the right eyebrow," says Bowe, adding that it'd make her look more awake and her face would be more harmonious.

To treat typical creases (usually frown and forehead lines) for someone in her early 30s, Bowe would use 25 to 30 units per treatment every three to six months, depending on how pronounced the lines are. If you were (or are) a smoker, or someone with a lot of sun damage, Bowe says you may require a few more units.

Annual Cost: $1,800 to $2,700

Laura, pictured right, is proof that age isn't always the best test for when you need Botox. Bowe says she looks younger than her age (35), and can probably hold off on preventative Botox for another three to five years.

Diagnosis: Bowe does note that Laura might benefit from Botox under each eye to treat what derms call the "jelly roll" -- the roll of skin that forms under the eye when some people smile. "By treating that, her eyes will stay more widely open when she smiles," says Bowe.

Treatment: In a few years, Bowe says that a patient who is a "smiler" like Laura might benefit from a drop of Botox to lift her eyelids and eyebrows, as well as a few drops to smooth out her crow's feet. For now, one unit under each eye every three to four months would give Laura a more wide-eyed smile, a request Bowe receives from patients of all ages.

Annual Cost: $120 to $160

"I have yet to meet someone over 40 who couldn't benefit from Botox, Dysport or Xeomin," says Bowe.

"A lot of patients come in and they're so proud that they waited until they really couldn't stand it, or they held out for longer than their friends. And I tell them that if they had come in five years earlier, we could have done just a few injections -- but now, for the same result, they're going to need a resurfacing laser and three different procedures, which is going to cost more money," says Bowe.

Diagnosis: Bowe says that Jill, 41, has a few issues: namely, crow's feet and frown lines. "Between her eyebrows, you can almost see the belly of the muscle and where it undulates," says Bowe. Her forehead, however, looks good, which is unusual for most women in their 40s.

Treatment: In addition to treating Jill's frown lines, Bowe says, "I'd do a few injections for her crow's feet and upper eyelids, the latter of which are starting to get heavy. A lateral brow lift with strategic injections at the tail of her eyebrows and around the crow's feet would really open up her eyes."

Annual Cost: Bowe says the recommended procedures would take between 25 and 45 units per session, which she recommends doing every three to four months -- putting the yearly cost somewhere between $1,350 and $2,880.