Note 11 - Business Segment Information - Segment Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Revenue from Contract with Customer, Including Assessed Tax	$ 2,777,000	$ 5,014,000	$ 6,046,000	$ 9,773,000
Stock option expense	(492,000)	(539,000)	(1,107,000)	(1,027,000)
Depreciation	(36,000)	(38,000)	(78,000)	(72,000)
Research and development expense	(535,000)	(623,000)	(1,324,000)	(1,407,000)
Operating income (loss)	(1,802,000)	(890,000)	(3,664,000)	(1,653,000)
Interest income (expense)	(80,000)	(2,000)	(145,000)	(14,000)
Tangible assets	11,121,000		11,121,000		$ 9,056,000
Operating lease right-of use	937,000		937,000		992,000
Finance lease right-of-use	418,000		418,000		451,000
Investment in South Korean joint venture	23,000		23,000		14,000
Total	12,499,000		12,499,000		10,513,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	23,000		23,000		14,000
Segment Reporting, Reconciling Item, Corporate Nonsegment [Member]
Stock option expense	(292,000)	(476,000)	(701,000)	(905,000)
Depreciation	(10,000)	(10,000)	(19,000)	(19,000)
Research and development expense	(219,000)	(214,000)	(466,000)	(537,000)
Operating income (loss)	(1,045,000)	(1,124,000)	(1,858,000)	(2,369,000)
Interest income (expense)	3,000	(2,000)	6,000	(5,000)
Tangible assets	797,000		797,000		775,000
Operating lease right-of use	299,000		299,000		333,000
Finance lease right-of-use	0		0		0
Total	1,119,000		1,119,000		1,122,000
Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	23,000		23,000		14,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue from Contract with Customer, Including Assessed Tax	2,006,000	4,012,000	4,809,000	8,586,000
Depreciation	(10,000)	(8,000)	(23,000)	(13,000)
Operating income (loss)	823,000	1,490,000	1,780,000	3,288,000
Interest income (expense)	33,000	6,000	47,000	4,000
Tangible assets	6,932,000		6,932,000		5,879,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	6,932,000		6,932,000		5,879,000
Operating Segments [Member] | Odor-No-More [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BioLargo Engineering, Science & Technologies, LLC [Member]
Revenue from Contract with Customer, Including Assessed Tax	940,000	1,259,000	1,630,000	1,615,000
Depreciation	(11,000)	(18,000)	(28,000)	(36,000)
Research and development expense	(82,000)	(336,000)	(326,000)	(688,000)
Operating income (loss)	16,000	(247,000)	(364,000)	(692,000)
Tangible assets	1,128,000		1,128,000		790,000
Operating lease right-of use	638,000		638,000		659,000
Finance lease right-of-use	0		0		0
Total	1,766,000		1,766,000		1,449,000
Operating Segments [Member] | BioLargo Engineering, Science & Technologies, LLC [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | Clyra Segment [Member]
Stock option expense	(200,000)	(63,000)	(406,000)	(122,000)
Depreciation	(3,000)	(2,000)	(4,000)	(4,000)
Research and development expense	(229,000)	(100,000)	(564,000)	(213,000)
Operating income (loss)	(1,263,000)	(616,000)	(2,580,000)	(1,154,000)
Interest income (expense)	(116,000)	(6,000)	(198,000)	(13,000)
Tangible assets	2,441,000		2,441,000		1,696,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	418,000		418,000		451,000
Total	2,859,000		2,859,000		2,147,000
Operating Segments [Member] | Clyra Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BioLargo Energy Technologies, Inc (BETI) [Member]
Depreciation	(2,000)	0	(4,000)	0
Research and development expense	(54,000)	(133,000)	(113,000)	(220,000)
Operating income (loss)	(122)	(226)	(217)	(388)
Tangible assets	39,000		39,000		46,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	39,000		39,000		46,000
Operating Segments [Member] | BioLargo Energy Technologies, Inc (BETI) [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BEST [Member]
Operating income (loss)	(67,000)	(49,000)	(125,000)	(115,000)
Tangible assets	0		0		0
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	0		0		0
Operating Segments [Member] | BEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BioLargo Canada [Member]
Revenue from Contract with Customer, Including Assessed Tax	0	0	8,000	0
Research and development expense	(120,000)	(97,000)	(256,000)	(177,000)
Operating income (loss)	(144,000)	(118,000)	(300,000)	(223,000)
Tangible assets	6,000		6,000		104,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	6,000		6,000		104,000
Operating Segments [Member] | BioLargo Canada [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Including Assessed Tax	(169,000)	(257,000)	(401,000)	(428,000)
Research and development expense	169,000	$ 257,000	401,000	$ 428,000
Tangible assets	(222,000)		(222,000)		(234,000)
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	(222,000)		(222,000)		(234,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	$ 0		$ 0		$ 0