What is the most likely diagnosis for a rash that appears as dark tan patches with a reddish cast and fine scales, notably on a young construction worker's back, arms, and neck?

The description of the rash as dark tan patches with a reddish cast and fine scales, particularly in a young construction worker, aligns well with tinea versicolor. This condition, also known as pityriasis versicolor, is a fungal infection caused by an overgrowth of yeast that naturally occurs on the skin. It often manifests as lighter or darker patches that can be tan, brown, or even reddish, which may not tan appropriately with sun exposure, especially in areas that have been sun-exposed, such as the back, arms, and neck.

Tinea versicolor is more common in young adults and those with increased sun exposure, such as a construction worker. The fine scales that may become more apparent when the affected skin is scraped or stretched can help to confirm this diagnosis clinically.

Other conditions such as psoriasis and actinic keratosis present with different characteristics. Psoriasis typically appears as well-defined red plaques with silvery-yellow scales and does not commonly present in a manner consistent with the tan patches described. Actinic keratosis, on the other hand, tends to appear as rough, scaly patches that are usually associated with sun exposure but do not generally present with the fine scales and reddish cast described. Alopecia areata involves hair loss