indurations

Induration is a medical term describing the process of becoming or the state of being hard or firm in consistency. In clinical examination, induration refers to a palpable area of tissue that is unusually firm, often detected by touch. It is distinct from edema, which is soft and may be swelling, and from erythema, which is redness of the skin.

Induration can arise from several processes, including inflammation with subsequent fibrosis, chronic infection, granulomatous disease, ischemic injury with scar formation, calcification, or neoplastic involvement. In the skin or subcutaneous tissues, induration may accompany conditions such as cellulitis, panniculitis, scleroderma, or scar formation. The size, depth, and borders of an indurated area help guide differential diagnosis and further testing.

In practice, induration is assessed by palpation, and in some contexts its presence or extent may influence the choice of imaging or histopathologic evaluation. For instance, indurated lesions may prompt consideration of fibrosis, granulomas, or tumor involvement rather than simple edema. While induration is a sign rather than a diagnosis, persistent, enlarging, or atypical indurated areas typically require further investigation, which may include imaging or biopsy.

In tuberculosis testing, induration specifically denotes the hard, raised area formed at the injection site after 48–72 hours; the measured diameter in millimeters is used to interpret infection risk thresholds, independent of redness.

The term derives from Latin indurare, “to harden.”