Last month’s call itself was routine, since it comes about six times a year. But what the New York Blood Center representative said this time, after asking me to make my next appointment, indeed threw me: “This will be your 100th blood donation.”

I know this benchmark is small potatoes compared to some donors’ numbers. Many people with decades on me, for instance, have given blood 200 times or more. And while the whole-blood donations I do are limited to once about every two months, donors of platelets — the part of the blood that aids in closing wounds — can give up to four times in that period.

Still, I’m part of just 7 percent of the population with Type O-negative blood, which makes me a universal donor. My father, certainly my inspiration, was a proud donor well into his 70s, and it has become second nature for me, too.

He might not have started as early, though. I was 17 and a high school senior when I first donated, and I listened closely to what the blood technician cautioned me against doing that day, including exercise. So of course, I took my tennis racket and a few balls to knock off the wall of the handball court … in the sun.

I nearly fainted — but learned a lesson the way kids often must.

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That and other early donations helped reassure me another day, a few years after that, when I and other U.S. Coast Guard buddies donated blood while stationed on Guam. One of us, Stuey, who had gone first behind the curtain while the rest of us waited nearby, deliberately let out an ear-piercing scream when the nurse inserted the needle — to spook the newbies who had never given blood.

Nobody that day skipped out; sometimes peer pressure is a good thing. That’s important long-term when you consider the reasons to take part:

It’s safe. Donors first complete a questionnaire, which screens out prospects with certain behaviors (recent tattoo?), particular illnesses, and even past travel to certain regions of concern. A phlebotomy technician performs a brief physical to take temperature and blood pressure, among other checks, before the actual donation. Each unit donated is a pint, one of about 10 you have in all, and your body begins to replenish it right away.

Related: The Blood Donors Who Saved Lives

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Post-donation, you’re led to a lounge with snacks and all the juice or coffee you want. The whole process takes about an hour — longer if you’re donating red cells or platelets rather than whole blood.

Concerned about dirty needles? By standard practices, you couldn’t become infected from a needle since all supplies are sterile and used only once. Another plus: Your blood is tested for HIV, hepatitis B and C, syphilis, and other infectious diseases before it’s released to hospitals, and you’re notified if there’s any cause for concern.

It’s convenient. Blood drives are invariably going on somewhere around you. Companies sponsor blood drives in which the local blood center sends representatives. So do churches, schools, community centers, and many other organizations. Another option is a trip to the blood center itself. Mine takes appointments, but I’m guessing they’d accept the occasional walk-in, too.

It’s lifesaving. Since donated blood is broken up into its components — red blood cells, plasma, and platelets — every unit can go toward three people in need. Red cells help patients with, say, trauma, chronic anemia, or internal bleeding. Plasma is for those with serious burns, severe liver disease, and other threats. And platelets help people undergoing chemotherapy or recovering from transplant surgery.

Related: How Three Troopers Saved a New Mom’s Life

There’s another benefit to giving blood: helping ensure that enough is available for emergencies. Less than 4 percent of the U.S. population donates every year, according to the American Red Cross, and you never know when you yourself might need it in a pinch.

This is one small way I know I make a real difference.

Stuey, probably not even 20 years old, learned that firsthand. A few short months after our unit’s blood drive, he swerved one of our forklifts abruptly on an unpaved slope — and tipped it over. His scream was real this time because the overhead-guard bar, meant to protect the driver in such cases, had landed on his arm just below the elbow. His limb dangled by a strip of skin no wider than a strand of fettuccine.

I never learned what happened to Stuey’s arm — or Stuey, for that matter. But I do know that every two seconds someone in the U.S. needs blood — because of disease, burns or accidents like this one. I never feel I’m giving enough time, money or items to the typical charity. This is one small way I know I make a real difference.