sich die Haare föhnen

You need to use the reflexive pronoun sich. This changes based on who is doing the drying. If I do it, I say ich föhne mir. If you do it, it's du föhnst dir. Notice that we use mir and dir (dative case) because the hair is the direct object. It’s a great way to practice your reflexive verbs in a low-pressure setting. Just remember: the person doing the action receives the benefit of the dry hair!

Use this anytime you are talking about your grooming routine. It’s perfect for explaining why you are running late. You might use it when chatting with a roommate. It’s also common when talking about getting ready for a big event. If you are at the gym, you might ask where the hairdryers are. In a hair salon, the stylist will definitely ask if you want a blow-dry.

Don't use föhnen if you are just letting your hair air-dry. For that, use an der Luft trocknen lassen. Also, don't use it for drying other things. You wouldn't föhnen your wet clothes or a spilled drink. That would sound very strange to a native speaker. Stick to hair and you will be perfectly fine.

Germans are quite proud of their engineering, even in hair care! The word Fön was actually a registered trademark by the company AEG. It was named after the 'Föhn' wind, a warm wind in the Alps. Over time, the brand name became the common word for the device. Now, everyone uses the verb föhnen regardless of the brand they own. It’s a classic example of a brand name becoming a language staple.

You can be more specific if you like. You might say den Pony föhnen if you are just doing your bangs. If you are styling it professionally, you might hear glatt föhnen (to blow-dry straight). Some people just say die Haare machen (to do one's hair). However, föhnen remains the most precise and common term for the drying part.