What to bring to a cenote: the list they check

Most cenotes open to the public check you at the entrance. It isn't red tape: a cenote holds fresh water that moves very slowly through a cave system, and whatever goes in takes years to come out. That's why the banned list is short and they don't bend it.

In short

At the entrance they'll ask you to leave behind: sunscreen with oxybenzone or octinoxate, repellent — natural ones too — self-tanner, body oil and make-up.
What protects you in the water is fabric, not cream: a long-sleeved rash guard, which is what the guides wear.
Mineral sunscreen is for the journey: twenty minutes before you leave the house, then a quick shower before you get in.
A hat and sunglasses. Obvious, and always forgotten.
The order: sunscreen at home · covered up on the way · shower before going in · rinse and moisturise on the way out.

What they'll ask you to leave outside

Sunscreen with oxybenzone or octinoxate. This is the number one reason people get sent to the showers. On the label it reads exactly like that.
Insect repellent. Even the ones labelled natural. DEET and citronella are equally a problem in the water.
Tanning oil, body oil and make-up. Anything that forms a film floats and stays there.

What actually works

The practical rule is simple: whatever goes on your skin goes on early and gets rinsed off before you get in, and what protects you in the water is fabric, not cream.

A long-sleeved rash guard. It's what the guides wear. Sun protection without putting anything in the water, and nothing to reapply.
Mineral sunscreen for the journey. Zinc oxide filter, on twenty minutes before you leave, and a quick shower before you get in. It covers the drive, which is when the sun is actually hitting you.
Hat and sunglasses. Obvious, always forgotten.

The Beach Kit pairs the mineral sunscreen with what you use afterwards.

See the Beach Kit

The order of the day

At home: mineral sunscreen on face and body.
On the way: hat, rash guard.
At the cenote: shower before getting in, no exceptions.
Coming out: rinse, then something that hydrates — fresh water dries you out more than you'd think.

What almost nobody brings and then wishes they had

A quick-dry towel, sandals you don't mind soaking — wet limestone is genuinely slippery — and drinking water. Inside most cenotes there's nowhere to buy anything.

What people ask before they go

Do they really check at the entrance?

At most cenotes open to the public, yes — and several will send you to the showers before you go in. It isn't a token gesture: the water moves very slowly and whatever goes in takes years to come out.

Can I bring repellent if it's a natural one?

Not in the water. Citronella and essential oils form a film just like DEET does. Put it on when you come out, which is when the mosquitoes show up anyway.

What if I want to tan?

Tanning oils and body oils are on the banned list: they float and they stay. If you're going to be in the sun, you'll tan anyway with protection on — slower, and without the burn.

I turned up with the wrong sunscreen. Now what?

Three ways out, in this order: shower thoroughly and don't reapply; cover up with a long-sleeved top and a hat; or buy an approved one at the park shop.

See cenote-safe protection · What the label has to say