If someone is struggling to breathe, passes out, or their heart stops, CPR is one of the best ways to keep them alive until medical help can arrive. However, CPR is dangerous to attempt if you don't have any training. Here's how you could end up hurting more than helping.
The concussive force of pushing on someone's chest to encourage breathing and for their heart to start can actually hurt them. It's not unheard of for the ribcage to be broken during CPR attempts, even if someone does have training. Without it, you won't know how much pressure to apply. Too little will have no effect and won't help to circulate blood through their body, but too much could severely injure them. This could make survival even harder. If the person makes it, they'll have to cope through recovering from broken bones and internal bruising. In either case, it's not a great help to the person who needs CPR.
Another common mistake is giving mouth-to-mouth resuscitation without any CPR training. CPR training teaches you how to give air to another person, when to stop, and how frequently to do it.
The lungs can't expand infinitely, which means that if you exhale too much air into another person's lungs, things can turn ugly fast. The lungs can potentially burst if inflated too far. When this happens, it becomes impossible to process air and transfer it through the body. If done incorrectly, trying to give mouth-to-mouth could kill. In addition, you'll need to know what to look for to ensure that the lungs have cleared of air before you provide another breath.
Finally, the rhythm you provide CPR with is also important. When you're trained, you'll receive information on how to maintain a solid rhythm that encourages the heart to beat and restart. Unfortunately, without it, you could end up triggering arrhythmia.
Arrhythmia is when the heart essentially quivers but doesn't fully contract and release, which is necessary to send blood through the body. Doing chest compressions too fast can lead to this.
Taking CPR training is easy and can typically be completed with some classroom learning and a hands-on test. Knowing that you have the knowledge and practice under your belt to save another person's life in the event of an emergency is something you can take pride in. Consider taking CPR classes and get certified.