Note 11 - Business Segment Information - Segment Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Revenue from Contract with Customer, Including Assessed Tax	$ 4,760,000	$ 3,742,000
Stock option expense	(488,000)	(256,000)
Depreciation	(36,000)	(22,000)
Research and Development Expense	(784,000)	(565,000)
BioLargo corporate	(763,000)	(477,000)
Interest income (expense)	(12,000)	(48,000)
Tangible assets	8,735,000		$ 7,094,000
Right of use, operating lease, net of amortization	1,068,000		1,092,000
Investment in South Korean joint venture	18,000		19,000
Total	9,821,000		8,205,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	18,000		19,000
Segment Reporting, Reconciling Item, Corporate Nonsegment [Member]
Stock option expense	(429,000)	(195,000)
Depreciation	(10,000)	(6,000)
Research and Development Expense	(314,000)	(189,000)
BioLargo corporate	(1,244,000)	(799,000)
Interest income (expense)	(3,000)	(36,000)
Tangible assets	1,079,000		942,000
Right of use, operating lease, net of amortization	380,000		394,000
Total	1,477,000		1,355,000
Segment Reporting, Reconciling Item, Corporate Nonsegment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	18,000		19,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue from Contract with Customer, Including Assessed Tax	4,575,000	3,543,000
Depreciation	(5,000)	(4,000)
Research and Development Expense	0	0
BioLargo corporate	1,798,000	1,387,000
Interest income (expense)	(2,000)	(2,000)
Tangible assets	5,870,000		4,624,000
Right of use, operating lease, net of amortization	0		0
Total	5,870,000		4,624,000
Operating Segments [Member] | Odor-No-More [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0
Operating Segments [Member] | BLEST [Member]
Tangible assets	734,000		1,083,000
Right of use, operating lease, net of amortization	688,000		698,000
Total	1,422,000		1,781,000
Operating Segments [Member] | BLEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0
Operating Segments [Member] | Clyra Medical [Member]
Tangible assets	949,000		432,000
Right of use, operating lease, net of amortization	0		0
Total	949,000		432,000
Operating Segments [Member] | Clyra Medical [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0
Operating Segments [Member] | BioLargo Energy Technologies, Inc (BETI) [Member]
Research and Development Expense	(80,000)	(32,000)
BioLargo corporate	(155,000)	(87,000)
Tangible assets	65,000		4,000
Right of use, operating lease, net of amortization	0		0
Total	65,000		4,000
Operating Segments [Member] | BioLargo Energy Technologies, Inc (BETI) [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0
Operating Segments [Member] | BEST [Member]
BioLargo corporate	(66,000)	0
Tangible assets	0		0
Right of use, operating lease, net of amortization	0		0
Total	0		0
Operating Segments [Member] | BEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0
Operating Segments [Member] | BioLargo Canada [Member]
Research and Development Expense	(80,000)	(135,000)
BioLargo corporate	(105,000)	(184,000)
Tangible assets	38,000		50,000
Right of use, operating lease, net of amortization	0		0
Total	38,000		50,000
Operating Segments [Member] | BioLargo Canada [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0
Operating Segments [Member] | BioLargo Engineering, Science & Technologies, LLC [Member]
Revenue from Contract with Customer, Including Assessed Tax	356,000	363,000
Depreciation	(19,000)	(2,000)
Research and Development Expense	(352,000)	(245,000)
BioLargo corporate	(445,000)	(368,000)
Operating Segments [Member] | Clyra Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	0	6,000
Stock option expense	(59,000)	(61,000)
Depreciation	(2,000)	(10,000)
Research and Development Expense	(121,000)	(134,000)
BioLargo corporate	(546,000)	(426,000)
Interest income (expense)	(7,000)	(10,000)
Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Including Assessed Tax	(171,000)	(170,000)
Research and Development Expense	163,000	$ 170,000
Tangible assets	0		(41,000)
Right of use, operating lease, net of amortization	0		0
Total	0		(41,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	$ 0		$ 0