A major activity favored by many tourists in Cancun: sun bathing
Most hotels offer camastros or lounge beds, along with parasols and bar/snack services at the beach. These services are normally exclusive for hotel guests, or you can buy a day pass which also gives you the right to use the pool, pool towels and may include food.
These day passes have become quite expensive and way out of reach for many locals. In fact, allthough the beaches are public according to Mexican law, the hotels have made it their business to close the entrances to the beaches. The hotels are private property and they won't let you go through to get to the beach. As a result, the few beaches that remain accessible are often hopelessly crowded with families looking to spend a sunday afternoon enjoying themselves.
Most tourists won't realise this, but for many people living in Cancun sunbathing at the beach is becoming more and more restricted. As a Mexican (I'm not but let's say I am for the sake of the argument) I could go to your hotel's beach and spread my towel between your hotel's beach beds. I guarantee you that in no time I'd have a security guard on my back asking me not too politely to move on. I can argue, of course, that the sand is federal property and thus public. But would you subject yourself to this humiliation? Most people just stay away and that's exactly the intention.
That doesn't mean you shouldn't enjoy Cancun sun bathing at the beach, though. You've probably worked hard and earned yourself a welcome vacation. I just want to show you the flip side of all this development in Cancun. Sunbathing is nice, just know that you are privileged and count your blessings with gratitude.
This question keeps popping up in travel forums about Cancun:
Is topless sunbathing allowed? Can I go topfree?
Topless women are regarded as somewhat mundane, I guess. For many Mexicans, nakedness or sexuality is still a very delicate issue, even taboo. Just to give you an example, my friend Tine has a woman who cleans her house. This woman brings along her 4-year old son along to play with Tine's, and she gets completely upset when the kids play in the pool in their adam's costume, while whe ourselves tend to not make a point of it. After all they're just small kids. Anyway, in general you won't see many Mexican women take off their top at the beach.
However, beaches are public and in Cancun, sunbathing topless women are welcome. If someone tries to convince you it's not allowed don't let yourself be intimidated. It's probably an overactive security guard. Wether or not topless women are allowed at the hotel pool is a different story. That depends totally on hotel policy since hotels are private property.
Since I found the issue intrigueing I've called a number of hotels and most of them told me they are not topless friendly. "European style" at the pool is in most cases a no-no. Many family hotels are understandibly concerned about kids having run-ins with topfree sunbathers. At the Riu Palace you have to lie face down so that nobody sees your breasts.
These are a few that apparently* allow topless sunbathing at the pool:
So, at the beach it seems more a question of consensus. Do you feel comfortable taking off your top? Look around the first few days and see if there are more women topfree. But know that it's not prohibited.
There are no nude beaches in Cancun, nor in Playa del Carmen As far as I know there´s no beach anywhere on the Yucatan peninsula that's officially declared a nudist beach. Because all beaches are public and federal property according to Mexican law. That doesn't mean you can't either. You'll just have to go and find a quiet beach away from the main tourist areas (you'll need a car).
Beaches in Tulum have been traditionally known as nude beaches, where nude sunbathers mix with topless women and people in swimsuit. Try the Copal cabañas if you're looking for a clothing optional lodging.