For decades, we’ve all been told to use expensive serums and SPF moisturizers regularly to keep our skin looking young and fresh. But skincare goes beyond anti-aging—according to the American Academy of Dermatology, an estimated 9,500 people in the U.S. are diagnosed with skin cancer every day. Prevention is key, but fortunately skin cancer is almost always treatable when caught early. So, with May recognized as Skin Cancer Awareness Month, we’re sharing key tips for spotting changes in your skin and when to call your doctor.

As a rule of thumb, you should conduct a self check of your entire body on a monthly basis to look for any abnormal moles, lesions, or other new changes to your skin color or texture. An easy way to remember what to look for is using the ABCDE rule: Asymmetry, Border irregularity, Color, Diameter, and Evolving appearance.

Asymmetry: Moles that are bigger on one side than the other are more often than not a cause for concern.

Border Irregularity: Is your mole smooth and round, or splotchy and uneven? Abnormalities in shape are characteristic of melanomas—take note and set up an appointment with your doctor.

Color: Just as with shape, color irregularities are a notable sign of cancer. If your moles are a solid, consistent color throughout, there is usually no need to worry. But if you see varying shades of brown, tan, black or even red or blue, you should have your dermatologist take a look.

Diameter: Large moles are typically a sign of melanoma—but what exactly does “large” mean? A good baseline measurement is the tip of a pencil eraser: if it’s smaller, it’s probably fine, but something larger could be melanoma.

Evolving Appearance: Once you spot an unusual mole be sure to track it over time. Does it change in shape, size or color? Any changes in appearance are a just cause for concern and should be brought to the attention of your doctor.