Because, it's more than "just a brow" when done properly. To ensure maximum comfort after waxing, Simon Says it is important to follow these guidelines:

• Avoid applying heat to the waxed area for 12 to 24 hours. This includes hot baths and steam.
• Use an anti-acne lotion following the treatment and twice a day until breakouts are gone. Use only an anti-acne product recommended by your skin care professional.
• Avoid suntanning for 12 to 24 hours. Seriously, don't burn your face off. This includes any strong UV light exposure or tanning beds.
• Avoid applying highly fragrant products to the waxed area. This includes, perfume, scented lotions, cosmetics or oils.
• Avoid using harsh, abrasive or exfoliating products in the waxed area; including Retinols, Benzoyl Peroxide or Salicylic. However, if you are prone to in-grown hairs, the day after your waxing treatment, manually exfoliate newly waxed area with a soft cloth or sponge or use Witch Hazel to avoid future problems. 
• Avoid applying high SPF sunblocks to the waxed area for 12-24 hours. Sunscreen chemicals can be irritating to the newly waxed skin. This includes self-tanning products and tan accelerators.
• Any pinking of the skin should disappear within 6 to 8 hours after the waxing treatment. Slight pinking is normal, and indicates that the hair was removed from the root, rather than superficially broken off, as in shaving. This is the reason that professional waxing lasts so much longer.