Also heard: "I wear sunscreen every day."

Why you should fess up: If you aren't honest about regularly baking in the sun or roasting on a tanning bed, it makes it harder for your doctor to detect skin cancer early on. Simzar says most of the patients he sees lie about about sun exposure they've accumulated or tend to leave out noticeable chunks in their tanning bed history. According to Simzar, a physician informed with your true tanning habits will be better equipped to find suspicious lesions and samples to send over to the lab for analysis -- something that could mean the difference between life and death.

Other lies that float around a derm's office have to do with conveniently overestimating hand-washing frequency and sunscreen use, underestimating picking at the face and leaving out past products and procedures, all of which affect the outcome of prescribed medications and how well or soon your skin will start to heal according to Dr. Andrea Paul, the chief medical officer of BoardVitals in New York. For example, high levels of retinol can make skin more sensitive to the sun and more susceptible to tearing. "I once saw a patient who was using retinol on her face and had a waxing done, but failed to disclose to them and to me that she was using a retinol product," says Paul. The end result wasn't pretty. Retinols chemically slough off the outer layer of dead skin cells, meaning the wax wasn't just ripping out hairs, but it took living skin cells along with it.