Hooded seals are sexually dimorphic with males being larger than females. Male hooded seals also have a black, crescent shaped, inflatable nasal sac that when flacid droops down over the muzzle. With one nostril closed, male hooded seals can also inflate their nasal septum through the opposite nostril, producing a large red balloon-like structure. Both are used in courtship and dominance displays. Females lack these secondary sexual characteristics.
Females give birth to one pup yearly on pack ice, away from the edges of ice floes.
Pups are weaned in just four days, the shortest time for any mammal. There are currently no reliable abundance estimates for either stock although previous estimates for each stock were on the order of 500,000 individuals. Currently there are insufficient data to assess the status of either stock. Hooded seals are hunted throughout their range and, considering the unknown status of both stocks, exploitation and international trade may constitute a threat to the species. This may be especially true where hunting is not well regulated.