Primary microplastics come from household products. Think about things like deodorant or toothpaste. They leave behind a residue, which when it breaks down becomes a mircoplastic. These plastics are intentionally designed to be small.
Secondary microplastics on the other hand are sourced from debris, such as degrading packaging, paints on plastic, or fibers. These are plastics that start off big, but over time get smaller and spread throughout the environment.