LONDON — They’re tiny, colorful and harmless-looking, but these little pellets are being blamed for causing big problems for the world’s oceans and seas.

The items in question are plastic microbeads, and on Tuesday, Britain made good on a pledge to ban the manufacturing of personal care products containing them.

So what are these pellets, and what’s all the fuss about?

What are microbeads?

Microbeads are itty-bitty plastic orbs that can be found in exfoliating facial scrubs, shower gels and toothpaste, among other products. They are part of a larger class of microplastics, or pieces of plastic less than five millimeters, or 0.2 inch, long. (Roughly the size of a grain of rice.)

Microplastics exist elsewhere, too. They can be found in chewing gum, industrial cleaning products, synthetic clothing fibers and tires.