A method of enabling an analysis taking into account exposure of at least one external body portion to the environment comprises obtaining first information representative of at least one condition of a first external body portion of a subject and obtaining second information representative of at least one condition of a second external body portion of the subject. The method further comprises determining a difference between the first information and the second information so as to enable an analysis taking into account impact of at least one environmental factor. The second external body portion is normally less exposed to at least one environmental factor than the first external body portion.