Śivasaṃhitā 2.25

Iḍā is the lunar channel of the subtle body, carrying a cool, receptive, and feminine quality of energy. Its path begins at the base of the spine, ascends along the left side, and crosses to terminate at the right nostril. This counterintuitive crossing is not incidental — it mirrors the contralateral organization of the nervous system and reflects the deeply interwoven nature of polar energies.

The name iḍā has ancient Vedic roots, where it referred to a nourishing offering or a goddess associated with refreshment and abundance. Its adoption into tantric anatomy transforms this meaning: iḍā now nourishes the subtle body, irrigating the energetic system with prāṇa of lunar (candra) character — cooling, stabilizing, and inward-drawing.

In prāṇāyāma practice, particularly nāḍīśodhana (alternate nostril breathing), Iḍā is engaged by inhaling through the left nostril. Yogic tradition recommends that when Iḍā predominates, one undertake contemplative study, meditation, or rest. Its harmonization with Piṅgalā is the prerequisite for prāṇa to enter and ascend through Suṣumṇā.