Mottled skin with a crusty or scaly appearance is caused by sun exposure, and is common in elderly populations, reports Healthline. Individuals with a history of sunburns, or with light skin and blue eyes are at an increased risk of developing these sun spots later in life.
Crusty, discolored skin is often caused by sun exposure and is known as actinic keratosis, according to Healthline. This condition is a result of abnormal growth of keratinocytes, which cause the excess pigmentation and crusty appearance. These spots are actually forms of squamous cell carcinomas, and often 10 percent of these spots become invasive over time. This condition can be prevented through avoiding the midday sun and the regular use of sunscreen.
Other causes of scaly skin rashes include viral infections, such as chickenpox or allergic reactions, adds Everyday Health. Reactions to specific drugs may cause skin reactions as well. Intertrigo can cause crusty skin spots, as the skin becomes raw between skin folds and then falls to bacterial infections. Eczema can be characterized by dry or scaly skin patches, and is caused by skin sensitivities to specific fabrics or soaps. Contact dermatitis, such as that caused by poison ivy, may result in large patches of irritated, blistered and scaly skin. If the reddened and scaly skin patch surrounds an ulcer, a staph infection may be to blame.