Are Harry, Ron, and Hermione using hand sanitizer after their dragon ride?

Question

There is a scene in Harry Potter and the Deathly Hallows: Part 2 that I was wondering about.

The scene is before the Battle of Hogwarts just after Harry, Ron, and Hermione disembark from their dragon chauffeur. The three of them jump into a lake and swim to the shore (Harry has a vision of Voldemort while they are swimming).

Once on the shore, Hermione seems to be dripping something onto their hands while they are talking and they rub them together. What is she dripping onto their hands and what is it supposed to do?

Seems like an odd time for hand sanitizer...

Here is a link to the scene starting where I describe:

Answer 1

In the book, the enchantments in the Lestrange vault at Gringotts resulted in them receiving a number of burns when the objects multiplied and made contact with their skin.

'It burned me!' moaned Hermione, sucking her blistered fingers.
'They have added Gemino and Flagrante Curses!' said Griphook. 'Everything you touch will burn and multiply, but the copies are worthless - and if you continue to handle the treasure, you will eventually be crushed to death by the weight of expanding gold!'
_{Harry Potter and the Deathly Hallows, Chapter 26 - Gringotts}

After escaping on the dragon and disembarking in the lake, they use essence of ditany to treat the burns and other injuries they'd received during the break-in at Gringotts.

It was the first time that he had seen them properly since escaping from the vault. Both had angry red burns all over their faces and arms, and their clothing was singed away in places. They were wincing as they dabbed essence of dittany onto their many injuries.
_{Harry Potter and the Deathly Hallows, Chapter 27 - The Final Hiding Place}

In the movie, this particular part of the book may have been modified to remove the burning, which would cause the scenes following the dragon ride to appear totally out of place. This isn't that surprising since the movies are, on the whole, nonsense and result in a lot of things being unclear.

Answer 2

To supplement Anthony Grist's excellent answer, I'd like to address the film version of what happened.

What can be mistaken for hand sanitizer is actually essence of dittany.

Dittany is a magical plant used in Potion-Making, and is a powerful healing herb and restorative. Its use makes fresh skin grow over a wound, and after application, the wound seems several days old.

We even see it used in Deathly Hallows part 1. In the film, it's a bottle whose lid has a sort of eye dropper to administer little drops of essence of dittany to the wounded area of the body. Ron got splinched during apparition and needed dittany for healing.

In the film Deathly Hallows part 2, their hands had gotten torn up from holding on for dear life to the scales on the dragon's back for so long, without any protection for their hands. It's like riding a sprinting horse for a long time without a saddle, you're gonna need some ointment for the rashes afterwards. So, whether or not the gold from the vault had burned them in the film version, the extended period of holding onto the dragon's back barehanded would certainly call for a few drops of dittany.