Hi,
This could be duet contact dermatitis. Contact dermatitis is an inflammation of the skin caused by direct contact with an irritating or allergy-causing substance (irritant or allergen).
Irritant dermatitis, the most common type of contact dermatitis, involves inflammation resulting from contact with acids, alkaline materials such as soaps and detergents, solvents, or other chemicals. The reaction usually resembles a burn.
In some cases, although there may be no initial reaction, repeated use can cause eventual sensitization and reaction to the product. This would be the reason the tattoo is now causing the rash.
You can use a mild corticosteroid ointment to help reduce inflammation. This can only be used for a brief period till the rash subsides. Do not wear or apply anything on the site of the rash since this can aggravate the rash. You can take anti-histamines when it itches.
ref:http://www.myonlinewellness.com/topic/adam1000869
Also, when ever I wear my Uggs my foot seems to be really itchy wear my tattoo it. I've worn Uggs before I got my tattoo (& of course I'm not wearing them not seeing that it's summer) but what should I do when winter comes?