Hand sanitizers. Those ubiquitous bottles of clear gel come in a variety of sizes, scents, and colors and can be found in purses, cafeterias, and hospitals. According to the bottle, hand sanitizers kill 99.9% of illness-causing germs—nothing short of magic in a bottle.

Except that it isn’t. While hand sanitizers do a darn good job of protecting against illness, they aren’t the cure all some germaphobes hope for.

Fact 1: You have to do it right

Believe it or not, there is a right and wrong way to apply hand sanitizer, and many people do it wrong. First of all, the hand sanitizer has to contain at least 60% isopropyl or ethyl alcohol to be effective. Time matters, too. You have to have enough sanitizer on your paws to last for twenty seconds or more. Spend less time rubbing, and germies are still on your hands. Remember that when your kid scrubs for two seconds and wipes the rest on your jeans.

Fact 2: They don’t last forever

How long are your hands sanitized once you’ve slathered that miracle gel on your hand? As you may remember from high school science class, alcohol evaporates quickly. If you scrub for twenty seconds, the rest of the alcohol will have evaporated after thirty seconds. You are protected from new germs for approximately two minutes. Those two minutes might protect you from the germs on the doorknob, but it won’t protect you for an entire trip through the mall.

Fact 3: Some germs know better

Hand sanitizers will kill the germs on your hand, but they don’t differentiate. This means that your hand sanitizer will obliterate the good germs that help protect your skin, too. In addition, there are some germs that hand sanitizers just won’t kill. People have gotten icky bugs like E. coli and norovirus even after using hand sanitizer.

Fact 4: They can’t replace soap and water

Yes, hand sanitizer is great for those times when soap and water aren’t available, but they will never entirely replace the traditional approach to hand washing. Sanitizers were created to disinfect hands, not to clean. Hand sanitizer won’t do much for stickiness, dirt, or boogers. Despite the inconvenience, there are times you have to bite the bullet and find the nearest sink.

Fact 5: Watch out for irritation

Overuse of hand sanitizers can lead to redness and irritation, and some people are more sensitive to them than others. Go easy on the amount you use during the day, and follow up with a soothing lotion.

Fact 6: Despite everything else, it really is safe for kids

You’ve no doubt heard about the dangers of kids ingesting hand sanitizer and getting “drunk.” Apparently the Texas Poison Control Center did too, because they ran the numbers. What did they find? A two-year-old child would have to ingest a minimum of four teaspoons of hand sanitizer before experiencing toxicity. A quick lick of hand sanitizer isn’t going to do much damage, particularly since it’s evaporating quickly once it hits the hand. But parental supervision is still advised.