In general, today's contacts are much more comfortable than those of the past, but not everyone can-- or should-- wear them, for a variety of reasons. If you have chronically dry eyes, an infection of the lid or cornea, or you have trouble physically manipulating contact lenses, you may not be able to wear them. If you have an allergy that makes your eyes itch and swell, or you have extremely sensitive eyes, that can be a problem, as well. Some people don't like the thought of having a foreign body resting on their eye, and that can rule them out as a candidate for contact lenses. Another concern is the time it takes to adapt to wearing certain kinds of lenses. All daily-wear lenses-- whether hard; rigid gas-permeable, known as RGP (R-G-P); or soft-- have the inconvenience of needing to be properly cleaned and sterilized, as well as having to be inserted and removed. There's also the necessity for regular care, checkups, and good eye hygiene. Specific types of lenses have advantages and disadvantages. Hard lenses and RGPs have a longer break-in time and require consistent wear to maintain adaptation. They can slip off the center of your eye more easily than other types, and debris can easily get under them. Daily-wear soft lenses don't correct all vision problems, especially astigmatism, and your vision may not be as sharp as with RGP or hard lenses. They also require regular office visits for follow-up care. Extended-wear and extended-wear disposable lenses, which you wear overnight, also don't correct all vision problems and require regular office visits and monitoring. There's also an increased risk of medical complications, especially from corneal ulcers. One final concern is that all contact lenses need replacing, either from use or if you lose one, and they can be expensive.