Note 12 - Business Segment Information - Segment Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Revenue		$ 2,432,000	$ 1,861,000
Operating loss		(7,583,000)	(6,696,000)
Interest expense		(1,923,000)	(3,996,000)
Research and development		(1,338,000)	(1,472,000)
Tangible assets		2,729,000	1,728,000
Investment in South Korean joint venture		63,000
Intangible assets		2,150,000	1,893,000
Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture		63,000
Corporate, Non-Segment [Member]
Revenue		14,000
Operating loss		(3,947,000)	(3,651,000)
Interest expense		(1,823,000)	(3,944,000)
Research and development		(754,000)	(892,000)
Tangible assets		603,000	1,050,000
Intangible assets		2,150,000	1,893,000
Corporate, Non-Segment [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture		63,000
Operating Segments [Member] | Odor-No-More [Member]
Revenue		1,568,000	1,459,000
Operating loss		(493,000)	(335,000)
Interest expense			(2,000)
Tangible assets		624,000	420,000
Intangible assets
Operating Segments [Member] | Odor-No-More [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | Clyra Medical [Member]
Tangible assets		1,125,000	3,000
Intangible assets
Operating Segments [Member] | Clyra Medical [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | BLEST [Member]
Tangible assets		314,000	264,000
Intangible assets
Operating Segments [Member] | BLEST [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | BioLargo Water [Member]
Revenue		37,000
Operating loss		(697,000)	(728,000)
Research and development		(505,000)	(610,000)
Tangible assets		105,000	50,000
Intangible assets
Operating Segments [Member] | BioLargo Water [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture
Operating Segments [Member] | Clyra Segment [Member]
Revenue		240,000
Operating loss		(1,827,000)	(1,233,000)
Interest expense		(100,000)	(50,000)
Research and development		(164,000)	(219,000)
Operating Segments [Member] | BioLargo Engineering, Science & Technologies, LLC [Member]
Revenue		1,050,000	999,000
Operating loss		(619,000)	(749,000)
Research and development		(351,000)	(354,000)
Consolidation, Eliminations [Member]
Revenue		(477,000)	(597,000)
Research and development		436,000	603,000
Tangible assets	[1]	(42,000)	(59,000)
Intangible assets	[1]
Consolidation, Eliminations [Member] | Investment in South Korean Joint Venture [Member]
Investment in South Korean joint venture	[1]

[1] the "elimination" column reflects the net adjustment for receivables and payables generated between our related entities that are eliminated in consolidation.