Commonly caused by cold weather temperatures.
May also be caused by exiting the shower into a cold draught - referred to as 'RAPID chilly chap stick'
May be relieved using many methods:
moving to a warmer environment is most common. However, if one is unable to do this then the individual may have to seek other methods of resolution e.g. watching pornography, masturbation, reading erotica, putting on many layers of underpants (thick woolly undergarments are best insulators), introduing a warm (not hot as it can cause extensive damage, and we wouldn't want that!) application to the inguinal/genital area e.g. hot (remember, never actually 'hot') water bottle.
One may experience acute chilly chap stick in which case the penis returns to a 'normal' (very subjective) size after a few mintues.
Chronic chilly chap stick can be worrying and embarassing for the individual and should be handled with sensitivity. Medical advice may be required if attempts to resolve chronic CCS does not produce results.
a.k.a. artic pecker