Note 12 - Business Segment Information - Segment Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 19, 2019
Revenue from Contract with Customer, Including Assessed Tax	$ 5,884,000	$ 2,531,000
Research and development	(1,319,000)	(1,367,000)
Operating loss	(5,390,000)	(6,778,000)
Interest expense	(53,000)	(234,000)
Net loss	(5,132,000)	(6,894,000)
Net loss	5,132,000	6,894,000
Tangible assets	3,958,000	2,522,000
Operating Lease, Right-of-Use Asset	867,000	453,000	$ 399,000
Investment in South Korean joint venture	33,000	48,000
Total	4,858,000
Finite-Lived Intangible Assets, Net, Ending Balance		3,023,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	33,000	48,000
Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	5,000	7,000
Research and development	(674,000)	(1,001,000)
Operating loss	(3,971,000)	(5,688,000)
Interest expense	(24,000)	(118,000)
Net loss	(3,995,000)	(5,781,000)
Net loss	3,995,000	5,781,000
Tangible assets	669,000	555,000
Operating Lease, Right-of-Use Asset	136,000	222,000
Total	838,000
Finite-Lived Intangible Assets, Net, Ending Balance		825,000
Corporate, Non-Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	33,000	48,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue from Contract with Customer, Including Assessed Tax	4,374,000	1,419,000
Operating loss	1,130,000	(511,000)
Net loss	(1,304,000)	511,000
Net loss	1,304,000	(511,000)
Tangible assets	2,064,000	451,000
Operating Lease, Right-of-Use Asset	0	0
Total	2,064,000
Finite-Lived Intangible Assets, Net, Ending Balance		451,000
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] | Clyra Medical [Member]
Tangible assets	631,000	816,000
Operating Lease, Right-of-Use Asset	0	0
Total	631,000
Finite-Lived Intangible Assets, Net, Ending Balance		816,000
Operating Segments [Member] | Clyra Medical [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0	0
Operating Segments [Member] | BLEST [Member]
Tangible assets	441,000	595,000
Operating Lease, Right-of-Use Asset	731,000	231,000
Total	1,172,000
Finite-Lived Intangible Assets, Net, Ending Balance		433,000
Operating Segments [Member] | BLEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0	0
Operating Segments [Member] | BioLargo Water [Member]
Revenue from Contract with Customer, Including Assessed Tax	1,000	12,000
Research and development	(565,000)	(486,000)
Operating loss	(714,000)	(616,000)
Net loss	(604,000)	(566,000)
Net loss	604,000	566,000
Tangible assets	194,000	152,000
Operating Lease, Right-of-Use Asset	0	0
Total	194,000
Finite-Lived Intangible Assets, Net, Ending Balance		152,000
Operating Segments [Member] | BioLargo Water [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	1,943,000	1,635,000
Research and development	(469,000)	(488,000)
Operating loss	(452,000)	(629,000)
Net loss	(425,000)	(629,000)
Net loss	425,000	629,000
Operating Segments [Member] | Clyra Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	56,000	139,000
Research and development	(110,000)	(66,000)
Operating loss	(1,383,000)	666,000
Interest expense	(29,000)	(116,000)
Net loss	(1,412,000)	593,000
Net loss	1,412,000	(593,000)
Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Including Assessed Tax	(495,000)	(681,000)
Research and development	499,000	674,000
Tangible assets	(41,000)	(47,000)
Operating Lease, Right-of-Use Asset	0	0
Total	(41,000)
Finite-Lived Intangible Assets, Net, Ending Balance		(47,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	$ 0	$ 0