Cyanobacteria (blue-green algae), that are common inhabitants of water and terrestrial environments throughout the world, produce a broad spectrum of secondary metabolites - biologically active products that could be toxic (cyano?toxins). Scientific literature data unequivocally showed adverse effects of cyanotoxins on animal and human health, above all their hepatotoxic and neurotoxic activities. However, the cutaneous adverse effects of cyanobacteria and their cyanotoxins are often under-diagnosed, misdiagnosed or under reported together with a long-standing lack of knowledge about it, not only amongst primary healthcare providers, but also amongst dermatologists. The seaweed dermatitis is the first described cutaneous adverse effect that occurred after contact with marine waters in cyanobac?terial toxic bloom condition. This acute irritant dermatitis was connected with the benthic marine filamentous cyano?bacterium Lyngbya majuscula (Gomont) and its toxins (debromoaplysiatoxin, aplysiatoxin and lyngbyatoxin A). Apart from irritant cutaneous adverse effects, the hypersensitivity immune responses were reported as well, i.e. allergic con?tact dermatitis due to cylindrospermopsin from Cylindrospermopsis raciborski. Aside from direct or indirect (airborne dermatitis) local effects of cyanotoxins on the skin and/or mucous membranes, a severe systemic manifestations were also diagnosed, such as hay fever, asthma and generalized urticarial rash, as well as ocular symptoms and signs e.g., itchy edematous eyelids associated with conjunctivitis. Potentially toxic cyanobacteria and their toxins are present in water resources of the Republic of Serbia, which means that an adequate, relevant and more-coordinated monitoring of all water environments is crucial for preventing human exposure to cyanobacteria and their toxins. A significant role in all of these could and should be taken by dermatologists, above all in the identification of the cyanobacterial adverse effect on skin and mucous membranes, as well as in diagnostic allergy testing.