I do hollywoods all day long 
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If you're not a regular waxer, be prepared for some quite early regrowth. It can take 2 or 3 waxes for all the hair to get into the same growth cycle. After a couple of waxes you should get 6 weeks between appointments - so 2-3 weeks completely hair free with minimal regrowth after that.
In the days leading up to your appointment, exfoliate gently, it'll help pop out any ingrown hairs. You can carry on exfoliating gently from about 3 days after your wax to help prevent ingrowns.
Pop a painkiller about 45 mins before your appointment.
Don't trim! I do that for my clients if it needs doing. Some people that have trimmed themselves have trimmed too short.
Make sure your therapist is using a good hot wax (no strips) - Perron Rigot, Lycon or Berodins are the three best hot waxes. If they're using a good wax your skin will settle back to normal within a couple of hours.
Make sure they wear gloves, sanitise their hands before the treatment, and don't double dip - once the spatula full of wax has touched your skin they should be throwing it away and using a new spatula for each application of wax.
Try and relax (easier said than done ) and breathe. Afterwards no hot bath or shower for 24 hours, lukewarm is fine. No sauna, swimming or sunbathing for 48 hours.
And yes, I include the bum crack from top to bottom as part of my treatment.
You'll be fine!