Note 11 - Business Segment Information - Segment Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Revenue from Contract with Customer, Including Assessed Tax	$ 3,742,000	$ 965,000
Intersegment revenue	0	0
Research and development	(565,000)	(392,000)
Operating income (loss)	(477,000)	(1,710,000)
Grant income	31,000	5,000
Interest expense	(48,000)	(13,000)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(494,000)	(1,544,000)
Research and development	(565,000)	(392,000)
Operating income (loss)	(477,000)	(1,710,000)
Tangible assets	5,783,000		$ 3,958,000
Operating Lease, Right-of-Use Asset	837,000		867,000
Investment in South Korean joint venture	27,000		33,000
Total	6,647,000
Total			4,858,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	27,000		33,000
Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	0	2,000
Intersegment revenue	0	(2,000)
Research and development	(189,000)	(265,000)
Operating income (loss)	(799,000)	(1,220,000)
Grant income	0	0
Interest expense	(36,000)	(6,000)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(835,000)	(1,226,000)
Research and development	(189,000)	(265,000)
Operating income (loss)	(799,000)	(1,220,000)
Tangible assets	530,000		669,000
Operating Lease, Right-of-Use Asset	114,000		136,000
Total	671,000
Total			838,000
Corporate, Non-Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	27,000		33,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue from Contract with Customer, Including Assessed Tax	3,543,000	600,000
Intersegment revenue	0	(2,000)
Research and development	0	0
Operating income (loss)	1,387,000	13,000
Grant income	0	0
Interest expense	(2,000)	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	1,385,000	187,000
Research and development	0	0
Operating income (loss)	1,387,000	13,000
Tangible assets	3,392,000		2,064,000
Operating Lease, Right-of-Use Asset	0		0
Total	3,392,000
Total			2,064,000
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]
Revenue from Contract with Customer, Including Assessed Tax	6,000
Intersegment revenue	0
Research and development	(134,000)
Operating income (loss)	(426,000)
Grant income	0
Interest expense	(10,000)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(436,000)
Research and development	(134,000)
Operating income (loss)	(426,000)
Tangible assets	578,000		631,000
Operating Lease, Right-of-Use Asset	0		0
Total	578,000
Total			631,000
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]
Revenue from Contract with Customer, Including Assessed Tax	363,000	545,000
Intersegment revenue		(188,000)
Research and development		(108,000)
Operating income (loss)		(35,000)
Grant income		0
Interest expense		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		(35,000)
Research and development		(108,000)
Operating income (loss)		(35,000)
Tangible assets	505,000		441,000
Operating Lease, Right-of-Use Asset	723,000		731,000
Total	1,228,000
Total			1,172,000
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	0	0
Intersegment revenue	0	0
Research and development	(135,000)	(197,000)
Operating income (loss)	(184,000)	(228,000)
Grant income	31,000	5,000
Interest expense	0	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(153,000)	(223,000)
Research and development	(135,000)	(197,000)
Operating income (loss)	(184,000)	(228,000)
Tangible assets	223,000		194,000
Operating Lease, Right-of-Use Asset	0		0
Total	223,000
Total			194,000
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 Energy Technologies, Inc (BETI) [Member]
Revenue from Contract with Customer, Including Assessed Tax	0
Intersegment revenue	0
Research and development	(32,000)
Operating income (loss)	(87,000)
Grant income	0
Interest expense	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(87,000)
Research and development	(32,000)
Operating income (loss)	(87,000)
Tangible assets	628,000
Operating Lease, Right-of-Use Asset
Total	628,000
Operating Segments [Member] | BioLargo Energy Technologies, Inc (BETI) [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | Clyra Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax		10,000
Intersegment revenue		0
Research and development		(16,000)
Operating income (loss)		(240,000)
Grant income		0
Interest expense		(7,000)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		(247,000)
Research and development		(16,000)
Operating income (loss)		(240,000)
Operating Segments [Member] | BioLargo Engineering, Science & Technologies, LLC [Member]
Intersegment revenue	(170,000)
Research and development	(245,000)
Operating income (loss)	(368,000)
Grant income	0
Interest expense	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(368,000)
Research and development	(245,000)
Operating income (loss)	(368,000)
Intersegment Eliminations [Member]
Revenue from Contract with Customer, Including Assessed Tax	(170,000)	(188,000)
Intersegment revenue	170,000	192,000
Research and development	170,000	194,000
Operating income (loss)	0	0
Grant income	0	0
Interest expense	0	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	0	0
Research and development	170,000	194,000
Operating income (loss)	0	$ 0
Consolidation, Eliminations [Member]
Tangible assets	(73,000)		(41,000)
Operating Lease, Right-of-Use Asset	0		0
Total	(73,000)
Total			(41,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	$ 0		$ 0