Another recommendation for Headsweats. As mentioned, started using them to mitigate dripping sweat. Like gloves, won't head out without one. I use this one, (but in various side panel colors).

https://www.headsweats.com/super-duty-shorty-white-1/

I'm very thankful and grateful for this thread. As someone who takes a 1 blade to his noggin every week in a misguided attempt to try and disguise how thin his top is getting, and is also fairly new to riding more than just a few loops around the neighborhood with his kids, I never would have considered the sun getting through my helmet as we approach summer. I'll definitely be picking up a few head coverings for those mid-day rides.

But you're probably at an age where you could break your neck trying to look at your um... knees, yeah, knees. So get a good helmet. There have been a bunch of technological advancements in recent years as scientists have figured out what really causes head injuries. Definitely get a MIPS helmet. Bontrager (TREK) has started marketing helmets with a new material called WaveCell that intrigues me tremendously. Since I just replaced my helmet last year, I'm probably going to wait till next year to upgrade, but maybe not. I've suffered enough head injuries over my life that I don't want any more (but I don't want to stop doing dangerous things).
As far as the baldness goes, while I am :brag: still blessed with a full head of hair, my dermatologist insists I use sunscreen on my head if I'm going out. Just make sure to use a water resistant sport sunscreen. It stings when it runs into your eyes.

I bought a Giro Register MIPS - top rated by CR, seemed quite light, and MIPS (which seems to be a good idea). Tried it this weekend and loved compared to my clunky Berll.

I always wear a coolmax bandanna under the helmet to soak up sweat, shade my balding gourd, and keep me warm in the winter. Seems to work for me. Be Well, Bluesfrog

I've been using Headsweats Classics since 2013 to keep sweat from dripping into my eyes. I miss the checkerboard on my scalp, though.

I am bald and shave. I use a one of these helmets cheap from China. I like the fact that it is dual layered, which gives me confidence even if is not certified (others' confidence will vary), has a visor to which I attach my prescription lenses, and has a wire mesh that keeps out most of the sun and all insects and lets some air in.

I also use a pirate type cycling cap. These are cheap.

I'm a recent convert to skull caps. About a year and a hlf ago I was on vacation in Ecuador - at the equator and at 10'000 feet, and for the first time I got a sunburn on my scalp. I'm not bald, but I'm getting thin up there, particularly in the front. That was a wake-up moment for me. Now I don't ride without the skull caps. Like everybody says, they actually keep you cooler.

No sun screen above the eyes. I learned that one the hard way some time ago. I'm sure you all learned it too.

I shave my head daily and wear a cycling cap under my helmet. I don't use sun screen. To get my vitamin D, I time my rides for lower sun angle and around an hour a day. A handkerchief tucked under the back of the cap keeps the back of my neck from burning - for me a vulnerable spot. Finally getting my tan back slowly.

bike cap with the brim cut off.

Yikes! Last night I noticed a sharp border between helmeted and non-helmeted parts of my head, tanned face and half of forehead, untanned top of head.

Hey, I wear my cyclist tan as a badge of honor.

I like the Halo cap in summer and winter. In cold weather I have a cover on the helmet as well as the Halo cap on my head. In summer, it cools and prevents sunburn under the helmet.

I shave my head every morning. I wear a bike cap or one of those under armour skull caps, which I insert a handkerchief in the back to drape over my neck, where I usually get burns.

Not a lot of hair on my head either. Go to Amazon and type in "skull caps" or "doo rags" and take your pick. I bought a package of three for around $12-13 and they work just as good as the expensive Castelli skull caps that finally wore out.

Another fan of headsweats or similar here. Beware - the cheap ones that I've tried tended to be bulky and had seams that I could feel under the helmet. I easily outsweat the capacity of these things to absorb and evaporate perspiration, so focus on comfort and sun blocking ability.

Pro tip - you can cover the tops of your ears, too, and avoid some painful sunburn!

I'm bald on top and buzz everything else down to the lowest clipper setting. My helmet is a Giro with plenty of vents. I'm a total cycling cap convert. I have two different Walz caps, a regular cotton one, and a technical one. I actually prefer the cotton one--I feel like my helmet slides around on the tech one unless I ratchet my helmet so tight I have a dent in my forehead for the rest of the day. I live in Socal and it gets hot here, but I never really feel like the caps are making my head hotter. The visor is nice and I don't get the dreaded zebra stripe tan on my head.