Amazon is cultivating secret private brands, and it could be a problem for retailers everywhere

It turns out Amazon owns more secret brands than was originally clear.

Though we've known for a while that Amazon is creating a slew of private-label brands to complement its offerings from other retailers, the number of brands Amazon has in its own stable is larger than it previously let on.

Quartz counted 19 trademarks for brands that sell products on Amazon's website but give no immediate indication that the brand is owned by Amazon.

A further 10 brands were identified by Quartz as trademarks without products on Amazon.com, and a further eight brands are sold exclusively by Amazon but have no corresponding trademark.

The brands range from men's clothing and cleaning products to bed sheets and tools. For example, there's Arabella, which sells lingerie, and Single Cow Burger, which sells frozen foods.

An Amazon spokesperson confirmed to Quartz that some of the brands identified were indeed owned by Amazon.

The secrecy may suggest that Amazon has realized the limits of its name brand for selling merchandise. Using the Amazon brand may work well for selling cheap batteries - of which it maintains over 90% of the online market, according to UBS - but it may not be as effective in selling blouses and shoes.

Amazon's reputation has taken a hit from all sides recently as it moves into new categories and catches the ire of worker's rights groups. It's a prime target because of its size, just as Walmart was in the past, according to Business Insider's Kate Taylor.

This suggests that an explicitly Amazon-branded item might be less desirable, even if that item is being purchased on Amazon either way. This is especially true for clothing, which Americans often consider a more personal item.

This puts retailers in an even tougher spot than they were previously. Some holdouts, like Nike, who have avoided selling on Amazon in the past, have capitulated recently, and they now find themselves competing directly with Amazon's private labels.

The allure of the private label brand isn't new. It gives customers a cheaper option and a unique reason to shop from specific retailers. The trend of private-label brands complementing retailers' offerings has sped up in recent months, however, and with Amazon poised to put the pedal to the metal, it could spell trouble for some brands.