The life and photographic work of Lilo Hess has been very little studied and therefore consists of only fragmentary information gleaned from magazine articles and other short entries in publications about book illustrators, as well as her own published books and an obituary. Life magazine described her as a “specialist in animal photography” (Life 1943, 21). During the 1940s, her images were reproduced in Life, U.S. Camera, Popular Photography and others. Some of them were assignments for the PIX Publishing agency.

An illustration in Fotografische Rundschau in 1935 suggests that Hess's photographs were already being reproduced in magazines in Germany at this time. The photograph shows an African glutton poking its beak into the water at Berlin Zoo. The picture was taken with a Mentor camera equipped with a focal plane shutter, which allowed a very fast shutter speed and exposure time and thus enabled sharp images of fast movements. The picture was taken up close to the bird and at eye level, cutting out any reference to the zoo and giving the impression of a shot taken in the open air.

Before her emigration to New York in 1938, Hess grew up with her sister Trude (who later became art historian and emigrated via Rome to the US in 1935) in a Jewish merchant family in Berlin, where she developed her interest in zoology and graduated in this field. She later studied (commercial) photography at the Photographic School in Berlin (perhaps the Lette Verein) and at the Polytechnic School in London. Combining her interest in zoology and photography, she developed as an animal photographer. In London she “met a commercial photographer who had been assigned to make a children’s book about zoo animals. Although an excellent photographer, he lacked the patience required to take animal pictures and asked me to do the book for him” (Commie 1973, 111). The identity of the photographer and the title of the book are unknown. But Julian Huxley, the secretary of the Zoological Society in London, is known to have given commissions to a circle of other émigré animal photographers, such as Wolf Suschitzky and Ylla, during the 1930s. Huxley was also responsible for opening the children’s zoo at London Zoo. In 1938, Ylla provided the image for Julian Huxley’s book Animal Language. Ylla, who emigrated in 1941 to New York, where she set up her own studio, also took photographs at Bronx Zoo and published animal-related material, thereby operating in the same field as Lilo Hess,  but it is not known whether they were acquainted with each other. Lilo Hess was not the only photographer who had his first exile stop in London. Other photographers who stayed for a time in London before emigrating to New York City were Trude Fleischmann, Ellen Auerbach, Tim Gidal as well as Henry Rox.

Further evidence of Lilo Hess's involvement in the photographing of animals is her volunteering at the Museum for Natural History at the beginning of 1938 and the animal postcards and publicity pictures she produced in 1939 for the animal exhibitor and collector Frank Buck for his “Jungle Camp” show at the World’s Fair. Postcards and folders related to this show, however, contain no credits for Lilo Hess.

During her lifetime, Hess published more the 40 books – mainly for children – which included her animal photos, as well as own illustrations and writings. Her first children's book was Odd Pets (Crowell, 1951), following in 1954 with Cristine de baby chimpansee (G. Bell and Sons, 1954).
In the 1950s, she also participated in the Color Photography exhibition at the Museum of Modern Art (9 May – 4 July, 1950). It was one of the first colour photography exhibitions to be put on by Edward Steichen, the director of the Photographic Collection of MoMa. Other emigrated photographers who participated were: Erwin Blumenfeld, Josef Breitenbach, Fred Block, Andreas Feininger, Arthur Felling (Weegee), Fritz Goro (the husband of Carola Gregor), Herbert Gehr, Fritz Henle, Horst P. Horst, George Karger, Dimitri Kessel and Lisa Larsen, alongside their American colleagues Eliot Porter, Richard Avedon and many more.

Lilo Hess was married to Christopher William Coates, the director of the New York Aquarium, at Coney Island. Since 1964 they had been living on a 45‐acre farm in East Stroudsburg, where they had four ponies, two dogs, four cats and a wild fox.