There’s a rumor we’d like to end, here and now: Your odds of hair loss are not dependent on the genes inherited from your mother’s father.

Like anything else, genes from mom can play a role. But she’s only half the pie. You can also inherit these genes from your father, says Dr. Alan J. Bauman, Hair Restoration Physician and founder of Bauman Medical. “Hair-loss genes can be inherited from either your mother's or father's side of the family, or a combination of the two,” he says. He adds that there are roughly 200 different genes that regulate your hair growth, so the combination of these genes—from both parents—can be unique and won’t always pattern itself from one sibling to the next.

Decades ago, this would have been the most accurate way of determining your odds—looking at old photos of your ancestors—but now there are more scientific means of predicting hair loss. These days, your doctor can take a swab of DNA from the saliva inside your cheek, and it will show how sensitive you are to dihydrotestosterone (known as DHT, which is the hormone created by the body’s testosterone). This swab will also tell you your odds for balding (and how quickly), and can predict how you might react to hair-loss medications like Propecia or Finasteride treatment.

What Specifically Causes Hair Loss?

Hair loss can start as soon as puberty ends, depending on your hereditary sensitivity to DHT. That phrasing is key: Bauman stresses that it is not DHT production that causes hair loss, it's the inherited sensitivity to DHT that causes the loss. Those with high sensitivity will be the first to experience a weakening in their follicles. This results in thinning around the crown and hairline, and lighter pigment in the hair. Behaviors that increase DHT production will magnify the loss depending on sensitivity. These behaviors include smoking, creatine supplements, resistance and weight training exercise, stress, and taking anabolic steroids or testosterone hormone replacement.

How Hair Loss Progresses

One-fifth of men will experience significant hair loss by age of 20(!), and that percentage grows proportional to age. Bauman says that significant loss increases steadily with age: 30 percent will experience it in their 30s, 40 percent in 40s, and so on. “This math proves true for men into their 90s,” he says. “If you go unchecked but have maintained most of your hair by middle age, then your sensitivity to DHT is probably on the low side, meaning you have a slower rate of male pattern hair loss going on.”

Symptoms of gradual hair loss are sometimes hard to notice until nearly half the hair is gone. The most obvious signs are a thinning of the temples and hairline recession. Otherwise, the hair loss can be more widespread and balanced. This steady shedding is called “invisible baldness”, since the hair becomes gradually less dense until suddenly it is perceptible to the naked eye. “In general, hair loss is a chronic, progressive condition that gets worse over time without treatment,” Bauman says.

However, there are also ways to measure this “invisible baldness”. Bauman utilizes two procedures—HairCheck and HairCam—to track the hair-loss progression over time,. This periodic audit can soon paint your long-term hair-loss outlook by offering in-depth looks at density, recession, and more.

Also, you may have noticed that men, when they bald, never lose the hair around the sides and back of the head. Bauman says it is unknown why these follicles are immune to DHT, but this does explain why they’re the follicles used for transplants to increase coverage up top.

How to Strengthen Your Follicles and Slow Hair Loss

Regardless of your sensitivity to DHT, you will likely experience hair loss over time. It’s part of aging, says Bauman. Look at the odds: 90 percent of 90-year olds have experienced significant loss. However, you can slow down the fall-out rate, and not just with Propecia, Rogaine, and transplants.