When you buy secondhand, or have a lapse in washing, you will need to sanitise your MCN and other reusable items. Nursing pads, makeup wipes, cloth wipes, menstrual pads and underwear, cloth face masks, wool covers, and of course modern cloth nappies, all need sanitising at least once in their life cycle.
Sanitising your reusable items ensures they are no longer affected by ammonia or other bacterial nasties. You can also use the practices learned here to effectively manage household sicknesses.
This article will mention the use of bleach on MCN, and like anything; the dose makes the poison. Bleach, or sodium hypochlorite, is a very effective household cleaner when used correctly, and you should not be scared of it.
Sanitisation methods vary on fabric composition, machine type, and which chemicals you need to use.
If you own a front loader, a 90°c or 'boil wash' is the easiest for cotton, bamboo, hemp, and towelling. Anything containing PUL or wool cannot be washed at this temperature. For this you will need your items to be clean (post main wash), add your detergent amount for load level, and use the longest cycle time.
For top loader owners, or for PUL or ammonia infected wool items, you will need to bleach sanitise. This can be done on either a small or large scale. For a large scale sanitise, Clean Cloth Nappies (CCN) has developed a Front Loader Sanitise and an accompanying online tool to calculate exactly how much bleach to use for your machine and fabric type. This tool is behind a membership paywall, however, it is absolutely worth the price.
For small scale sanitises, Cloth Nappy Help have a great article on conversions using struckets and laundry tubs. This method requires more hands on effort, but is honestly great for sanitising smaller loads.
For wool that is simply secondhand, you can sanitise them with a laundry sanitiser such as Dettol or Canestan. I have linked the CCN page, 'Caring for Wool Covers', below incase the hyperlink doesn't work.