**Core Concept**
Atopic dermatitis, also known as eczema, is a chronic inflammatory skin condition characterized by dry, itchy, and scaly skin. It is a type of hypersensitivity reaction, often associated with allergies and genetic predisposition.

**Why the Correct Answer is Right**
The diagnosis of atopic dermatitis is primarily clinical, based on a combination of patient history, physical examination, and the presence of characteristic skin lesions. The criteria for diagnosis include a history of itchy, dry skin, and the presence of typical skin features such as lichenification, excoriations, and xerosis. The diagnosis is further supported by the presence of associated conditions such as asthma, rhinitis, and food allergies.

**Why Each Wrong Option is Incorrect**
**Option A:** Allergy testing is not a primary method for diagnosing atopic dermatitis, although it may be useful in identifying specific allergens that may trigger symptoms.
**Option B:** Biopsy may be helpful in ruling out other conditions that mimic atopic dermatitis, but it is not a primary diagnostic tool.
**Option C:** Patch testing is used to identify contact allergens, not to diagnose atopic dermatitis.

**Clinical Pearl / High-Yield Fact**
A key feature of atopic dermatitis is the presence of a personal or family history of allergies, which can include asthma, rhinitis, and food allergies.

**Correct Answer: D. Clinical evaluation and history.**