Not all ecommerce categories have caught on at the same rate. Buying toothpaste online is one thing. But shopping for lingerie, the most personal clothing item in a woman's closet? Not quite the same.

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And the reasons why are lessons that other ecommerce brand-categories can learn from.

First off, Lingerie is a $13 billion industry, growing at a rate of 3.3 percent each year. And, no surprise, Victoria's Secret dominates the market. Yet, while there has still been a huge rise in lingerie ecommerce startups, these up-and-coming lingerie brands face stiff challenges online.

Those challenges? There are the common ones all new brands face, of course, like gaining traffic, increasing trust and standing out in a noisy market environment. New lingerie brands, however, face another hurdle: cracking into a space whose companies have high rates of customer retention.

As Cora Harrington, founder of The Lingerie Addict, told me during an interview for Yotpo: “Once people find their favorite bra, they're reluctant to change.”

The reason revolves around concerns about assuring fit and comfort with an online purchase; and that's a big barrier to entry. A recent study of 1.3 million customer reviews connected to fashion ecommerce products found that the words shoppers most commonly use have to do with fit, quality, size and comfort.

And in no sector is this more true than lingerie. In the intimates industry, size really is personal -- it can vary from person to person, store to store and style to style. Ecommerce, Laura Mehlinger, founder of Lola Haze, told me, "is both a blessing and curse for lingerie brands.”

But online brands need not lose hope. “To overcome some of these challenges, online stores can offer very clear sizing guidelines and charts, as well as show photos of items from multiple angles so the customer can get a full sense of the item,” Mehlinger said.

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Another way brands can increase trust and solve common pain points like worries over fit and comfort is by offering pictures of the clothes on real customers. Lingerie-store owners can gather user-generated content (like customer photos, reviews, etc.) from current customers to use it to create Facebook ads (or any other social ads) -- a move that can result in an acquisition cost that's four times lower than that of normal Facebook ads with branded content.

In a Yotpo survey of 1,000 eCommerce shoppers, 77 percent of participants said that authentic photos from customers affected their purchase decisions more than professional photos from stores. In another survey, 40 percent of shoppers participating said that rich user-generated content (photos or videos) would most likely affect their purchase decisions.

A further aspect of the buying decision common to the lingerie industry is the plethora of dedicated online communities filled with participants eager to discuss the latest trends and brands in lingerie. (Make-up has similar communities)

In niche industries like these, therefore, it’s important for up-and-coming lingerie brands to get their items into the hands of the right influencers and prove themselves. Word of mouth spreads like wildfire in these communities, so great customer service is a must.

It’s vital for new brands to focus on building trust, and a solid reputation for great customer service. That effort starts from the moment customers land on your site and continues even after they’ve received their purchases. “As with all new brands, being responsive to customers is key," Mehlinger says. "A quick turnaround on answering customer questions, as well as having a clear and easily navigable website, will help customers trust the brand."

Brands also need to think ahead when it comes to customer service, so as not to lose them; customers are quick to judge. “Most customers won't email you for clarification -- they'll just go to a competitor,” Harrington, of The Lingerie Addict, told me.

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For lingerie brands -- and all brands -- attempting to break into a crowded space, it's imperative to focus on acquisition and retention. And one of the best strategies here is to turn current customers into brand advocates, social proof that satisfying customers increases the chance that new visitors will convert.