Photo-sensitive sunblock ad

What a great use of photochromic ink (ink that changes colour when exposed to light). This clever little ad is for Sundown Sunblock, by DDB Brasil.  The original form is a pale couple on the beach, the man (obviously NOT wearing sunblock) reddens when exposed to direct sunlight. This type of ink, as well as thermochromic ink (heat sensitive) can be pricey, but a creative solution looking for a problem. Once manufacturer of these inks is CTI Inks.