• Applying eyeliner inside the lashes  -  Coloring inside can bring bacteria into your eye and clog the oil secreting glands that protect your cornea.
• Sharing making up with friends - cross-infection is the result.  To avoid this, do not use old makeup and don’t share makeup with others.
• Re-wetting mascara - if you have to re-wet your mascara  it is too old and could contain bacteria.
• Using eye shadow powder that gets into your eyes - If your eyes are sensitive, try a cream eye shadow instead of powder. The cream will last longer and prevent powder pieces from getting into your eyes.
• Not cleaning your makeup brushes and eye pencils - not washing your brushes spreads bacteria, and even can lead to mold growing along the fibers of your brushes. Using old eye shadow brushes and old mascara spreads bacteria and dirt onto your eyelashes, eyelid margins and therefore tear film and possibly onto your cornea. Not sharpening your eye shadow pencils - Just like you clean your brushes regularly, sharpen your pencils on a regular basis to keep bacteria away.
• Sleeping with your makeup on - You will end up with dry eyes and bacteria in your eyes. Failing to wash off mascara or eyeliner is only going to increase the chances of bacterial and oil build up with eyelid inflammation. 
• Wearing extra long eyelashes - extra-long lashes are what most women prefer, but they have been shown to act as a wind-tunnel forcing air and particles directly into your eye making them drier and dirtier.
• Continued use of eyelash extensions - According to a recently released study by the British College of Optometrists, the repeated use of eyelash extensions can cause traction alopecia, a condition where the hair falls out due to excessive tensions place on the hair shaft.” Take a break every few months and let your bare lashes breathe; one of these lash conditioners will help repair any damage.
• Using mascara until it runs out - Replacing your mascara regularly is incredibly important to avoid eye infections.
• Using makeup that is old - makeup that’s past its prime becomes a breeding ground for bacteria and can lead to breakouts, infections, pink eye, and the list goes on.

All eye mascara takes is a single use to contaminate a mascara wand. Eye shadow and eye liner meant for the outside of the eyelid rather than the waterline are much safer. Aside from the risk of bacterial contamination, another potential hazard with mascara is scratching. A jab in the eye from a mascara wand or eyeliner pencil can scratch the cornea, and any dry, flaky, and powdery makeup that gets in the eye can cause redness, irritation, and swelling.

Particles in mascara as well as liquid eyeliner can also get into the small oil producing pores along the length of the eyelid margin and block them. These Meibomian gland pores produce the essential oil required for a stable tear film. Blocking these pores causes a chronic inflammatory reaction in the eyelid called posterior meibomitis which is the most common cause of red eyes, dry eyes and irritated eyes.

To reduce your risk of infection, discard mascara every 3-6 months, depending on your usage.  If you notice the mascara formula gets clumpy or starts to smell funny, which means it is bad, toss it out sooner rather than later.  And, remember to remove eye makeup at night.  Sleeping in eye makeup is only going to increase the chances of bacterial and oil build up with eyelid inflammation.  

The Food and Drug Administration reports that the most common injury from cosmetics comes from scratching the eye with a mascara wand. Eye scratches, if left untreated, can cause infections which, in turn, can lead to ulcers on the cornea, loss of lashes, or even blindness.