If you’re here because you’re dealing with a bruised fingernail, I can relate: One casual Saturday years ago, I was getting out of the car for a much-needed shopping trip with friends and completely smashed my thumbnail in the car door. When I looked down at my finger, I saw lots of blood and a huge crack across my entire nail. For the next 30 minutes, my friends and I raced around the mall looking for a Band-Aid and some Advil (Note: I’ve kept a first aid kit in my car ever since).

After the bleeding finally stopped, I was left with a cracked and bruised fingernail. My first inclination was to cover up the ugly wound with a gel manicure. (Yes, that’s my vanity showing.) But it turns out, that is the worst thing to do.

What that experience taught me is that I have a lot of questions about what to do when I've injured a fingernail. I know I’m not the first person to slam a finger in a car door or jam it in a window, so I took my questions to the professionals to get all the answers, from basic first aid to the right way to cover up a bruised fingernail or other nail mishap. Here’s what you need to know.

What causes nail bruising?

Like the bruises you get on any part of your body, nail bruising happens when blunt force crushes the small blood vessels under your skin, per U.S. National Library of Medicine. Most fingernail injuries affect the nail plate (the hard part of the nail that grows out), which can crack and potentially fall off, and the nail bed (the skin underneath the nail plate), which can bleed and bruise. So when we’re discussing a nail bruise, we’re really talking about a nail plate bruise.

That said, what you might assume is a nail bruise because of the purple or black color might actually be blood, since the same kind of trauma that causes bruising can cause bleeding too. The official name for this is a subungual hematoma, according to the American Osteopathic College of Dermatology. That pretty much just means a blood blister under the nail.

When the injury first happens, you can take care of any immediate first aid needs. Basic wound care applies here: Put pressure on the area to slow the bleeding if there is any, clean the wound with soap and water, apply a bandage, and take an analgesic to help with pain if needed. You can also ice your finger if you’ve got swelling in the area, dermatologist Ted Lain, M.D., tells SELF.

As you do all this, you should also assess the extent of the damage and whether or not a trip to the doctor is necessary. Speaking of...

There are a few things to look out for when it comes to deciding if you should see a doctor right after you injure your fingernail. Some signs include: 

Lack of blood flow: Press on a portion of the nail or finger that is not injured. If the area turns white and then turns pink within seconds when you release the pressure, you’ve got good capillary refill. That means blood is still flowing. If not, it’s a good idea to get it checked out.

Loss of sensation: You should also touch the tip of your finger to make sure you still have feeling in the area. “As long as you can feel everything, you probably don’t have any nerve damage,” says Dr. Lain.

Unusual colors in your fingertip: You also want to make sure the skin at the tip of the finger isn’t blue or blanched white—unusual colors are a sign you need to see a doctor.