When used and cared for correctly, wool is a long-lasting material. It does have certain requirements to maintain its properties and long service life. Pressure and abrasion are not good for wool - they don't make those elbow reinforcements just for show. Table edges are natural enemies of shirts made of wool.
Even a careful user may come to think of washing wool garments at some point. It's not a bad thought at all! Just wash it by hand with hand soap, right? Wrong. This isn't your usual "list of things you've been doing wrong"-article but do read on. There's a good chance you'll learn something new or get the good news that you're already doing things correctly.
Wool garments are usually such that they don't need to be washed. Undergarments from merino wool don't require washing unless they start to smell. Undershirts usually develop a smell in about a week of regular use, underpants and socks can go even longer as long as you air them every night.
So the first rule is to avoid it for as long as you can. Very often just airing the clothes does the trick and you should use your nose rather than count days to figure out whether the item requires washing or not. We've boldly used the same socks and underwear for quite long stretches of time without bad odors - washing the feet daily, of course.
If you're into optimizing, you can wear two shirts on alternating days: each shirt gets a long airing after one day of use. This should more than double the time between washes, as the shirt is used half as much and the usual airing during your sleep gets a whole day and another night added to it.
When washing wool garments and accessories, the biggest problem is felting and shrinkage, which is caused by the temperature difference between washing and rinsing waters. This is especially true when washing by hand under a faucet.
If your only option is to wash wool by hand, draw plenty of fresh water beforehand (30-40 liters or 10 gallons) and let it sit long enough for the temperature to equalize. The recommended temperature is 30 degrees Celsius (86° F) or lower. You can use hotter water, keeping in mind that hot water and agitation promotes shrinkage.
Virtually all washing machines have a wool cycle, which is more delicate compared to washing by hand. Most people don't have enough wool garments to fill the machine but you can use it below capacity - some machines even compensate for this. The wasted energy is more than offset by the fact that you wash wool items less often.
Merino wool is not as delicate as regular wool. We've sometimes washed merino socks and boxers along with cotton laundry at 60° C / 140° F and the universe didn't collapse. But they will last longer if you choose the correct program.
Avoid ordinary detergents and hand soap when washing wool. They are effective against greasy stains but also remove the necessary fats from wool fibers. Treating wool to these fats after washing is recommended in any case but it's better to not remove them unnecessarily in the first place.
Wool detergents include oils that treat the surface of wool fibers. This makes the fabric softer, reduces friction and wear between the fibers, and resists dirt, water, and odors.
If you use wool detergent and wool conditioner together, you can extend the time between washes after each time. There are recommended doses for the conditioner but you can add as much as you feel comfortable with. If you overdo it, just rinse the excess off and use a bit less conditioner next time.
Wool conditioners are commonly sold for baby clothes but can be applied to any wool items you wash. It improves wool's properties and as you don't wash wool that often, using the conditioner isn't an expensive practice.
Wool pilling happens when the fibers are broken through chafing, washing, and generally just wear. The broken ends of the fibers intertwine and form knots, which appear commonly to the sides of sweaters, cuffs, and inner arms. It can also happen to 100% synthetics, the key here is broken fibers, natural or not.
High-quality clothes have longer and stronger fibers, which makes them less prone to pilling. These include merino wool as well as alpaca wool. Also, if your wool fabric is sleek like on a suit (worsted to align and bind the fibers), pilling will take a longer time - but could still happen. Blends are more susceptible to pilling compared to 100% wool: even when polyamide or polyester makes the fabric more durable overall, the wool fibers break as easily as before.
To avoid pilling in the first place, choose clothes with high-quality materials, wash them with the appropriate program (not too hot, don't spin hard, not in a completely full machine, etc.), and avoid rubbing them, if possible.
While avoidance buys you a little time, you are definitely going to find pills on some of your clothes and they will look worn. That's where a wool comb comes in: the pills get caught in the net-like blade of the comb as you stroke along the knit.
You can do this with the garment laid on your thigh for example: pull the pilled area lightly taut and go gently over the pills. The comb does slightly wear the fabric in the process, so don't ham-fist it and don't use the comb as a daily routine.
Another way to use the wool comb is to place the garment on a table and use the comb at an angle you deem appropriate. This allows you to target just the pills and keep the blade off the knit itself.