Nummular Eczema
Nummular Eczema has three names, the first and most common being Nummular Eczema. The name Nummular Eczematous Dermatitis is the more formal medical description and the last being discoid eczema, because of the coin-shaped lesions that it forms.
Cause
The exact cause of the disease remains unknown, but one theoretical possibility of several irritation factors in combination to begin the onset of symptoms. If one where to change humidity environments and then exercise vigorously, the combination of the excess sweat and heat may irritate the sensitive skin.
Irritation (Things to avoid)
Some things that may irritate the skin initially or worsen the preexisting condition would be; wool clothing worn next the skin, topical medications, soaps that leave any type of residue such as scent, conditioners, oils, dyes, vitamins, extracts, or any other irregular ingredients, and laundry detergents which are scented or contain UV brighteners which are deposited into the fabric.
Appearance
Nummular Eczema usually starts as a small group of red spots (papules) then forms a blister like lesion called a vesicle.
Vesicles range from 2 to 10 centimeters in diameter and have an even red color across the surface which will sometimes become clear in the center, and begin to resemble a fungal condition called ringworm.
New acute lesions may “weep” a fluid that forms a crust, while older or recurring will look somewhat scaly.
Outbreaks of Nummular Eczema may start with one or several lesions, some might experience clearing within the year while others continue for several years, Recurring usually at the in initial outbreak site.
The most common site for Nummular Eczema to appear is the legs but is also known to form on the arms, hands, and torso.

Any type of treatment should only be done under the consultation of a dermatologist.