Comparison — DSM-5 Learning Lab

Onset / developmental pattern

Both can begin at any age; SSD often follows a period of genuine physical symptoms (which may or may not have a clear medical explanation), while IAD frequently follows a health scare, a family illness, or begins without an identifiable physical trigger at all.

Duration / course

Both require a persistent pattern (IAD: illness preoccupation for 6+ months; SSD: symptomatic state persistently, typically also 6+ months) rather than a brief worry.

Associated features

SSD's excessive thoughts/behaviors are anchored to specific bodily symptoms (pain, fatigue, GI complaints); IAD's worry is about the idea of illness itself and can persist even when no symptom is present to point to.

Functional impairment

SSD impairment often centers on the symptom itself limiting activity; IAD impairment often centers on the time, cost, and relational strain of reassurance-seeking (or, in the avoidant type, delayed necessary care).

Rule-outs / exclusions

The decisive question: is there a real, distressing somatic symptom driving the concern? If yes, and the response to it is excessive, SSD is more likely. If the worry exists largely independent of any actual symptom, IAD is more likely.

The differential question

Don't let 'this person worries a lot about their health' alone decide the diagnosis -- always check whether there's an actual somatic symptom anchoring the concern before choosing between these two.

Common student confusion

Students often treat these as the same disorder with different names. They aren't: SSD is fundamentally a symptom-focused disorder with an anxious/behavioral overlay; IAD is fundamentally an anxiety disorder about illness with little or no symptom anchor.

Case clues

If a case mentions a specific symptom (chronic pain, fatigue, GI upset) that's actually present and driving repeated evaluation, lean SSD. If the case describes worry about illness with essentially normal exams and no persistent symptom, lean IAD.

Distinguishing table

Feature	Illness Anxiety Disorder	Somatic Symptom Disorder
Anchor of the concern	The idea of illness, largely independent of actual symptoms	One or more real, distressing somatic symptoms
Response pattern	Reassurance-seeking or care avoidance	Excessive thoughts/feelings/behaviors about the symptom itself
What resolves it (temporarily)	A negative test or reassurance -- briefly	Symptom-focused excessive concern persists even when medically explained or unexplained

Clarifying questions to ask

Is there a specific physical symptom present right now, or is the worry about illness in general?
When a test comes back normal, how long does the relief last before the worry returns?
Do you find yourself avoiding medical care, or seeking it out repeatedly?

Read each disorder in full

Somatic Symptom and Related Disorders

Illness Anxiety Disorder

A preoccupation with having or acquiring a serious illness, in the absence of significant somatic symptoms, driven by anxiety about health rather than by the physical symptoms themselves.