There's no formula for who will get cancer.

People who have never smoked can get lung cancer, though smoking clearly raises the risk. Someone who lost her mom to breast cancer might never have an abnormal mammogram.

Most people realize that cancer is not contagious—you can't catch it from your sneezing co-worker.

But, when it comes to genetics and cancer, people are less informed and easily scared when, in reality, only a small percentage of cancers have genetic links.

Only 5% to 10% of all cancers are a direct result of genes inherited directly from a parent, says the American Cancer Society.

But, if you do have family members who have had cancer, your likelihood of developing it is higher than someone who doesn't have a family history.

So it's a good thing to know and share that information with your doctor.

What Causes Cancer?

Cancer is caused by cells in your body growing and multiplying out of control, according to the American Cancer Society. The DNA—the basic genetic material that makes you who you are—in cancer cells is damaged. These damaged cells then begin to multiply. We don't know what causes this, but smoking and sun exposure are obvious culprits.

Cancer & Genetics: A 3-Part Q&A

1) If my mom or dad had cancer, will I get it too?

That's not always the case.

Cancer's genetic component comes from mutated DNA. And you inherit DNA from your parents, who inherited DNA from their parents, and so on.

You cannot inherit cancer itself, but you can inherit the gene mutation that damages the cells. And that gene mutation can increase your risk of developing cancer.

Also, common living environments or lifestyle habits in families—like if many people in your family are smokers—can be the actual underlying cause of the cancer in families, according to the National Cancer Institute.

2) What should I do if my family does have a history of cancer?

As with any medical concern, your first step is to talk to your doctor.

Make sure you bring as much information about your family's cancer history as you can gather:

  • Who had it?
  • What type of cancer?
  • What age were they when they were diagnosed?
  • What were the outcomes?

You can use the Department of Health and Human Services' My Family Health Portrait online tool to keep track of your family's health history.

Your doctor may tell you not to worry or advise you to start screening for certain cancers earlier or more frequently.

Keep in mind that having a family history does not mean you will automatically develop cancer.

3) Should I have genetic testing?

For a recommendation tailored to you, talk to your doctor about your concerns and your family history.

The American Cancer Society (ACS) recommends that you consider genetic testing if:

  • Several of your family members (your mother, sister, aunt, etc.) have or have had cancer—especially if they all had the same type of cancer
  • You know that cancer in your family is linked to a gene mutation that you may have inherited, or there is a known genetic mutation in your family
  • Several relatives have developed cancer at age 50 or younger
  • Close relatives were diagnosed with rare cancers—such as von Hippel-Lindau syndrome, Li-Fraumeni syndrome, or multiple endocrine neoplasia—that are known to be hereditary cancers

Like most medical decisions you will make, working with a trusted specialist and having as much information as you can will help you stop worrying and decide what's best for you.