Companies are struggling to keep up with the demand for coloured pencils while the phenomenon of adult colouring continues.

Have you been spending your spare time colouring in the lines? If so, it might be time to stock up on your pencil crayons. The adult colouring book craze is surely leading to huge sales for coloured pencils. This trend might also be prompting a global pencil crayon "shortage".

When colouring books for adults became a worldwide trend of 2015, topping bookstores' bestseller lists, manufacturers of products like pencil crayons, markers and pens faced an unexpected increase in demand.

The Bavaria-based Faber-Castell was one of these companies, stating that they have "noticed the effects of the colouring trend very strongly." They even began running extra shifts in their factories in order to cope with the demand for pencil crayons.

Staedtler, another manufacturer and supplier of writing and drawing supplies, is in partnership with Johanna Basford, one of the pioneers of the adult colouring trend, who recommends their products. The company increased their sales by 14% in 2015, with additional staff appointed and extra machinery purchased to meet the global demand for pencil crayons.

Although we aren't seeing a coloured pencil shortage per se, manufacturers have had to adjust their schedules to make sure that they don't run out of supplies. They have had to meet new standards as "people are now not satisfied with ‘just' 36 colours" and they are also investing in higher quality products than ever before.

Colouring lovers might need to turn to paint, markers or crayons, though, in order to continue spending time colouring in the lines.