The rust, bronze, and gold castes are considered to be the "lowblood" castes (ahir lakyisi), though this term does not have any legal definition or implication. On average, lowbloods range from 5'2"-5'10" (157-189cm) at ten sweeps of age (hornless height), and can be expected to grow up to twenty-five percent taller as they approach seniority. Members of these castes all have potential for psychic conditions, which often plays a role in their placement in the workforce. Although rustbloods and bronzebloods don't show proclivity towards a specific type of psychic condition, goldbloods who do have a psychic condition will almost always manifest it as psionicism, which is congenital and immediately diagnosable by the solid color of their eyes and complete lack of visible pupils. Psionicism is only known to affect goldbloods.

Psionicism is a general diagnosis, and those who possess this condition, known as psionics, will usually only have one or two of the many possible symptoms associated with the condition. Symptoms include telekinesis, electrokinesis, telepathy, clairvoyance, precognition, and the most stereotypical yet uncommon optical discharge, otherwise known as "eye lasers".

Voidrot is a related condition which can occur in psionics who regularly exert their psionic abilities; it is not infectious, but it is spontaneous and begins first in the brain but can spread throughout the nervous system. Those affected by voidrot will gradually lose their cognitive capacities, primarily their psionicism, and suffer from great fatigue as their body attempts to provide nutrients to necrotic cells that refuse to heal. It can be treated through medication, radiation therapy, and electrotherapy, but total recovery from voidrot occurs only in around 7% of cases. Untreated voidrot is inevitably fatal.

Lowbloods are often assigned to the departments of Ground Conflict, Agriculture, Labor, Industry, and Engineering. The lowblood castes, in total, make up about half of the total galactic population, with rustbloods taking up a quarter of the total population alone.