Websites focused on caregivers — from nannies to those taking care of elderly parents — burst on the scene in the late 1990s, then fizzled out quickly among the many dot-coms with faulty business plans.

But in the past six months, three Boston-area companies have launched websites focused on that same online audience, and this time they’re faced with a new challenge: attracting users who don’t identify themselves as “caregivers.”

About 34 million adults in the U.S., or 16 percent of the population, provide care to people 50 or older. The average caregiver age is 47. And about 8.9 million caregivers look after someone at least 50 years old with dementia, according to the San Francisco-based Family Caregivers Alliance.