Of the top five beauty brands by market share, only Maybelline is associated with makeup exclusively. Judging by the other four brands (including Aveeno and Burt's Bees), it seems that skincare is more commonly bought on Amazon, likely due to items such as moisturizer, body wash or lip balm being bought on price and product attributes rather than subjective qualities like color or coverage.
This idea is reinforced by One Click Retail findings. In Q2 2018, nutrition and wellness and mass skincare were the top-selling product subcategories within health and personal care and beauty.
In an October 2018 CivicScience survey, more US women said they had made their last cosmetics purchase at a big-box store (21%) than those who reported shopping through other channels. This was followed by specialty retailers like Sephora or Ulta (17%) and drugstores (15%). Beauty retail sites and beauty brand sites were far less popular (3% each). Amazon was not mentioned specifically but would fall under "other" (8%).
It appears that online vs. offline beauty shopping is spurred by different motivations. The beauty buyers who valued quality most were far more likely to shop directly at a beauty brand site (64%), while big-box stores won shoppers on price (28%). Mysteriously, 61% shopped at an online beauty retailer for "other" reasons besides quality, price, reviews, brand or variety.
Rewards might have something to do with it.
Beyond price and store location (which doesn't apply to ecommerce), the most important factors for US female beauty buyers in choosing a store were special sales, unique products and rewards programs, according to a February 2018 Pymnts.com survey. Ulta.com, Sephora.com and SallyBeauty.com all carry products that are exclusive to each retailer, and many online beauty retailers offer free samples and membership perks like free shipping, exclusive sales and points redeemable for merchandise.