Final answer:
Seborrheic dermatitis is a relatively common skin disorder, especially when considering the high prevalence rates of other skin conditions like acne and eczema.
Step-by-step explanation:
Seborrheic dermatitis is a common skin disorder that mainly affects the scalp, but it can also occur in other oily areas of the body, such as the face, upper chest, and back. While the exact prevalence of seborrheic dermatitis is not explicitly provided, we can look at other skin disorders to gauge its commonality. For instance, acne is one of the most ubiquitous skin conditions, affecting nearly 80% of teenagers and young adults. Eczema is another widespread skin disorder that presents as a red, flaky rash and can occur at any age. Given that these skin conditions are very common and seborrheic dermatitis is also categorized among them, we can infer that seborrheic dermatitis is a relatively common condition as well.