Even if you’ve had a period for decades at this point, you might be wondering what’s “normal” and what’s not when it comes to your period blood color. Sometimes it’s bright red, but other times it’s brown, pink, and even black, orange, green, or gray — which could signal an infection or other health condition, such as early pregnancy, menopause, or possibly even a symptom of your hormonal birth control.

If you suddenly notice a hue that’s unusual to you (i.e., Why is my period blood brown?!), you might be wondering what the heck is going on and whether or not you need to see your doctor. Fear not, friends. We tapped an OB-GYN to break down why your period blood changes colors and how to know something’s not right.

A Quick Period Refresher

Even if it’s been a while since you’ve given it much thought, your menstrual cycle actually can tell you a lot about your overall health, says Dr. Jill Purdie, OB-GYN and medical director at Pediatrix Medical Group. So if you need a quick refresher on the 411 behind menstruation and why it changes color, no shame or worries here.

“Every month, the endometrium (lining of the uterus) grows and thickens in preparation and expectation of pregnancy,” Purdie tells Scary Mommy. “An embryo needs a thick lining in order to implant and grow. If no pregnancy occurs and no embryo implants, the body triggers the endometrium to shed,” a process which kickstarts your period.

Hormonal birth control methods prevent ovulation to prevent pregnancy, so you won’t have a “true” menstrual period when you use a hormonal contraceptive, such as the pill, patch, ring, and some IUDs. The blood you experience during the inactive period is your body’s reaction to the lack of synthetic hormones — more on this in a sec.

While periods surely can suck, your body is doing a lot throughout your menstrual cycle, and changes in blood and discharge often reflect that, says Purdie. “The endometrium does not all shed at one time,” which is why your bleeding likely occurs over the course of several days. “The amount that sheds varies throughout the period, which changes the consistency of the flow. The period blood changes in color as the amount of shedding changes.”

As for what that means IRL? “Lighter amounts of blood may appear more pink in the beginning and then become red as the bleeding becomes more active,” says Purdie. “The blood then becomes dark red or brown as the period goes on. The longer the blood is exposed to oxygen in the vagina, the darker it becomes. In other words, the longer it takes to leave the body, the darker it becomes.”

The Many Colors of the Period Rainbow

Now that you’ve got the, er, flow of a standard, healthy period, it’s understandable if you low-key panic to see something totally different, such as gray, green, orange, or even black blood. Before you freak, there are many reasons why your blood might look different day to day, and many of them are nothing to be terribly worried about.

Bright red blood generally represents new or more fresh blood that has had less time to oxidize, says Purdie, calling it “an indicator of active bleeding that typically occurs in the first 1-2 days of menstruation.” You might notice a redder hue with a heavier flow, so if your flow is suddenly extremely heavy (say, you’re bleeding through multiple pads, tampons, or menstrual cups per hour), checking in with your doctor isn’t a bad idea to rule out anything like an infection, uterine growths, or other reproductive concerns such as miscarriage.

You might notice pink bleeding at the very start of your period, which Purdie says usually occurs as the endometrium is just beginning to shed and will typically be followed by the aforementioned bright red blood. This happens when your period blood mixes with cervical discharge (aka mucus). But if you notice pink blood between periods, you might be dealing with another health concern, such as anemia or perimenopause. More commonly, pink blood is caused by things like ovulation (in which you might notice some light pink spotting); low-estrogen hormonal birth control (which can cause lighter, pink-hued periods); implantation bleeding (aka early pregnancy); and lochia, the postpartum discharge that consists of blood, mucus, and uterine tissue in the weeks after you give birth.

“Dark red, brown, or black bleeding is typically older blood, which occurs as menstruation comes to an end,” says Purdie. “This is common and normal in the vast majority of periods. If the bleeding is associated with significant pain or lasts longer than 10-14 days, this could be an indication that something is wrong.”

Rarely, black blood might indicate signs of a miscarriage or vaginal blockage (especially if it’s accompanied by fever, foul-smelling discharge, difficulty peeing, or vaginal irritation/swelling), so if you have any concerns, certainly give your doc a call to see what’s up.

“Typically, orange, green, or gray-colored bleeding is associated with vaginal infections,” says Purdie. “A person should assess for other symptoms of infections such as vaginal itching, irritation, odor, or pain.” Sometimes, though, orange-tinted blood could indicate early pregnancy, especially if you also notice pink blood around the same time and have no symptoms indicating infection.

When to See a Doctor

All of this is a lot, and it’s worth reiterating that if you ever feel concerned about anything medically, you should always check in with your doctor, who can answer questions and rule out anything serious. That said, there are a few telltale signs something’s amiss, as Purdie points out. Whether or not it’s accompanied by unusual color changes, you’ll want to give your doctor a call if:

• You’re bleeding for two weeks at a time, or your period comes every two weeks.
• You have to change a pad or tampon every 1-2 hours for more than two hours in a row.
• You have worsening pain not relieved by over-the-counter medications.
• Your period is accompanied by a fever.
• Your blood or discharge smells “foul.”

“Many people will have some nausea, vomiting, and diarrhea associated with their menstrual cycle,” says Purdie. “This can be normal, but if a person is unable to keep hydrated, they should discuss this with their doctor.” If your period is causing you intense, unmanageable pain, your doctor will help mitigate symptoms and get you back to feeling better ASAP.