Note 11 - Business Segment Information - Segment Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Revenue from Contract with Customer, Including Assessed Tax	$ 1,103,000	$ 4,351,000	$ 7,148,000	$ 14,122,000
Stock option expense	(844,000)	(237,000)	(1,951,000)	(1,264,000)
Depreciation	(34,000)	(39,000)	(112,000)	(115,000)
Research and development expense	(615,000)	(690,000)	(1,934,000)	(2,098,000)
Operating income (loss)	(7,180,000)	(1,061,000)	(10,844,000)	(2,715,000)
Interest income (expense)	(144,000)	(12,000)	(352,000)	(32,000)
Tangible assets	7,637,000		7,637,000		$ 9,056,000
Operating lease right-of use	1,070,000		1,070,000		992,000
Finance lease right-of-use	400,000		400,000		451,000
Investment in South Korean joint venture	23,000		23,000		14,000
Total	9,130,000		9,130,000		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	(651,000)	(194,000)	(1,352,000)	(1,099,000)
Depreciation	(9,000)	(9,000)	(28,000)	(28,000)
Research and development expense	(175,000)	(301,000)	(642,000)	(838,000)
Operating income (loss)	(1,172,000)	(798,000)	(3,034,000)	(3,165,000)
Interest income (expense)	(5,000)	(3,000)	(14,000)	(6,000)
Tangible assets	678,000		678,000		775,000
Operating lease right-of use	268,000		268,000		333,000
Finance lease right-of-use	0		0		0
Total	969,000		969,000		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	776,000	3,853,000	5,583,000	12,437,000
Depreciation	(11,000)	(10,000)	(34,000)	(27,000)
Operating income (loss)	(3,807,000)	1,382,000	(2,026,000)	4,668,000
Interest income (expense)	(1,000)	0	(4,000)	(4,000)
Tangible assets	2,565,000		2,565,000		5,879,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	2,565,000		2,565,000		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	450,000	824,000	2,080,000	2,439,000
Depreciation	(9,000)	(17,000)	(37,000)	(53,000)
Research and development expense	(222,000)	(157,000)	(541,000)	(845,000)
Operating income (loss)	(403,000)	(375,000)	(763,000)	(1,067,000)
Tangible assets	850,000		850,000		790,000
Operating lease right-of use	627,000		627,000		659,000
Finance lease right-of-use	0		0		0
Total	1,477,000		1,477,000		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	(193,000)	(43,000)	(599,000)	(165,000)
Depreciation	(3,000)	(3,000)	(7,000)	(7,000)
Research and development expense	(231,000)	(291,000)	(795,000)	(512,000)
Operating income (loss)	(1,483,000)	(857,000)	(4,063,000)	(2,019,000)
Interest income (expense)	(138,000)	(9,000)	(334,000)	(22,000)
Tangible assets	3,659,000		3,659,000		1,696,000
Operating lease right-of use	175,000		175,000		0
Finance lease right-of-use	400,000		400,000		451,000
Total	4,234,000		4,234,000		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	(6,000)	0
Research and development expense	(47,000)	(133,000)	(161,000)	(346,000)
Operating income (loss)	(128,000)	(194,000)	(346,000)	(575,000)
Tangible assets	87,000		87,000		46,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	87,000		87,000		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)	(83,000)	(59,000)	(208,000)	(174,000)
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	37,000	0	46,000	0
Research and development expense	(100,000)	(134,000)	(356,000)	(311,000)
Operating income (loss)	(104,000)	(160,000)	(404,000)	(383,000)
Tangible assets	1,000		1,000		104,000
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	1,000		1,000		104,000
Operating Segments [Member] | BioLargo Canada [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BLEST [Member]
Interest income (expense)	0	0	0	0
Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Including Assessed Tax	(160,000)	(326,000)	(561,000)	(754,000)
Research and development expense	160,000	$ 326,000	561,000	$ 754,000
Tangible assets	(203,000)		(203,000)		(234,000)
Operating lease right-of use	0		0		0
Finance lease right-of-use	0		0		0
Total	(203,000)		(203,000)		(234,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	$ 0		$ 0		$ 0