Note 11 - Business Segment Information - Segment Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Revenue from Contract with Customer, Including Assessed Tax	$ 2,672,000	$ 1,500,000	$ 7,860,000	$ 3,786,000
Research and development	(694,000)	(271,000)	(1,846,000)	(1,018,000)
Operating loss	(1,537,000)	(943,000)	(3,574,000)	(3,973,000)
Interest income (expense)	(12,000)	(14,000)	(72,000)	(42,000)
Tangible assets	5,753,000		5,753,000		$ 3,958,000
Operating Lease, Right-of-Use Asset	777,000		777,000		867,000
Investment in South Korean joint venture	15,000		15,000		33,000
Total	6,545,000		6,545,000		4,858,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	15,000		15,000		33,000
Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	0	2,000	0	4,000
Research and development	(234,000)	(140,000)	(665,000)	(570,000)
Operating loss	(797,000)	(783,000)	(2,230,000)	(2,925,000)
Interest income (expense)	(3,000)	(6,000)	(43,000)	(18,000)
Tangible assets	579,000		579,000		669,000
Operating Lease, Right-of-Use Asset	72,000		72,000		136,000
Total	666,000		666,000		838,000
Corporate, Non-Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	15,000		15,000		33,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue from Contract with Customer, Including Assessed Tax	2,513,000	1,199,000	7,374,000	2,499,000
Research and development	(14,000)	0	(14,000)	0
Operating loss	969,000	400,000	2,786,000	418,000
Interest income (expense)	(1,000)	0	(5,000)	0
Tangible assets	3,300,000		3,300,000		2,064,000
Operating Lease, Right-of-Use Asset	0		0		0
Total	3,300,000		3,300,000		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		0
Operating Segments [Member] | Clyra Medical [Member]
Tangible assets	1,202,000		1,202,000		631,000
Operating Lease, Right-of-Use Asset	0		0		0
Total	1,202,000		1,202,000		631,000
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	480,000		480,000		441,000
Operating Lease, Right-of-Use Asset	705,000		705,000		731,000
Total	1,185,000		1,185,000		1,172,000
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 from Contract with Customer, Including Assessed Tax	22,000	1,000	31,000	1,000
Research and development	(128,000)	(119,000)	(401,000)	(446,000)
Operating loss	(155,000)	(141,000)	(549,000)	(572,000)
Interest income (expense)	0	0	1,000	0
Tangible assets	89,000		89,000		194,000
Operating Lease, Right-of-Use Asset	0		0		0
Total	89,000		89,000		194,000
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 Energy Technologies, Inc (BETI) [Member]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Research and development	(537,000)	0	(840,000)	0
Operating loss	(559,000)	0	(943,000)	0
Tangible assets	144,000		144,000
Operating Lease, Right-of-Use Asset	0		0
Total	144,000		144,000
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] | BioLargo Engineering, Science & Technologies, LLC [Member]
Revenue from Contract with Customer, Including Assessed Tax	843,000	401,000	1,742,000	1,613,000
Research and development	(433,000)	(100,000)	(971,000)	(288,000)
Operating loss	(568,000)	(179,000)	(1,388,000)	(158,000)
Operating Segments [Member] | Clyra Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	14,000	17,000	20,000	34,000
Research and development	(68,000)	(31,000)	(262,000)	(73,000)
Operating loss	(427,000)	(240,000)	(1,250,000)	(736,000)
Interest income (expense)	(8,000)	(8,000)	(25,000)	(24,000)
Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Including Assessed Tax	(720,000)	(120,000)	(1,307,000)	(365,000)
Tangible assets	(41,000)		(41,000)		(41,000)
Operating Lease, Right-of-Use Asset	0		0		0
Total	(41,000)		(41,000)		(41,000)
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	0		0		$ 0
Intersegment Eliminations [Member]
Research and development	$ 720,000	$ 119,000	$ 1,307,000	$ 359,000