Note 9 - Business Segment Information - Segment Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Revenue	$ 1,323,000	$ 464,000	$ 2,287,000	$ 1,035,000
Operating loss	(1,321,000)	(1,702,000)	(3,031,000)	(3,560,000)
Interest expense	(15,000)	(89,000)	(28,000)	(182,000)
Research and development	(355,000)	(356,000)	(747,000)	(683,000)
Tangible assets	2,954,000		2,954,000		$ 2,522,000
Operating Lease, Right-of-Use Asset	390,000		390,000		453,000
Investment in South Korean joint venture	33,000		33,000		48,000
Total	3,377,000		3,377,000		3,023,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	33,000		33,000		48,000
Corporate, Non-Segment [Member]
Revenue	0	0	2,000	7,000
Operating loss	(923,000)	(937,000)	(2,143,000)	(1,860,000)
Interest expense	(6,000)	(51,000)	(12,000)	(106,000)
Research and development	(165,000)	(209,000)	(430,000)	(545,000)
Tangible assets	631,000		631,000		690,000
Operating Lease, Right-of-Use Asset	179,000		179,000		222,000
Total	843,000		843,000		960,000
Corporate, Non-Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	33,000		33,000		48,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue	700,000	318,000	1,300,000	638,000
Operating loss	11,000	(107,000)	18,000	(283,000)
Tangible assets	723,000		723,000		451,000
Operating Lease, Right-of-Use Asset	0		0		0
Total	723,000		723,000		451,000
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] | Clyra Medical [Member]
Tangible assets	799,000		799,000		832,000
Operating Lease, Right-of-Use Asset	0		0		0
Total	799,000		799,000		832,000
Operating Segments [Member] | Clyra Medical [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BLEST [Member]
Tangible assets	641,000		641,000		445,000
Operating Lease, Right-of-Use Asset	211,000		211,000		231,000
Total	852,000		852,000		676,000
Operating Segments [Member] | BLEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		0
Operating Segments [Member] | BioLargo Water [Member]
Revenue	0	0	0	9,000
Operating loss	(209,000)	(168,000)	(431,000)	(305,000)
Research and development	(130,000)	(138,000)	(327,000)	(257,000)
Tangible assets	179,000		179,000		152,000
Operating Lease, Right-of-Use Asset	0		0		0
Total	179,000		179,000		152,000
Operating Segments [Member] | BioLargo Water [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	670,000	266,000	1,213,000	654,000
Operating loss	56,000	(190,000)	21,000	(373,000)
Research and development	(80,000)	(123,000)	(188,000)	(228,000)
Operating Segments [Member] | Clyra Segment [Member]
Revenue	6,000	0	17,000	114,000
Operating loss	(256,000)	(300,000)	(496,000)	(739,000)
Interest expense	(9,000)	(38,000)	(16,000)	(76,000)
Research and development	(26,000)	(6,000)	(42,000)	(33,000)
Consolidation, Eliminations [Member]
Revenue	(53,000)	(120,000)	(245,000)	(387,000)
Research and development	46,000	$ 120,000	240,000	$ 380,000
Tangible assets	(19,000)		(19,000)		(47,000)
Operating Lease, Right-of-Use Asset	0		0		0
Total	(19,000)		(19,000)		(47,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	$ 0		$ 0		$ 0