The Curious Case of ‘Blue Bloods’: Why Do We Associate Nobility with This Color?

The term “blue blood” has intrigued people for centuries, often used to describe the nobility and aristocracy. Most famously associated with the regal lineages of Europe, it conjures images of grandeur and ancient pedigrees. The history of this peculiar expression is as colorful as the phrase itself, rooted in the social dynamics and physical appearances that differentiated the aristocratic class from the commoners.
It’s believed that the concept of ‘blue blood’ originated in medieval Spain, known as ‘sangre azul’, where it was attributed to the rich and powerful families. This idea was linked to visible blue veins, which appeared prominently against the pale skin of the wealthy, a physical trait not commonly found amongst those who worked outdoors and had more sun-exposed, tanned complexions. The visibility of their veins was also taken as a sign of their purported purity of lineage, a connection to their esteemed and uncontested ancestry.
Historical Origins of ‘Blue Blood’
The term ‘blue blood’ has an intriguing past, tightly interwoven with the fabric of medieval Spanish society and its class distinctions. Let’s explore how this term found its way from ancient aristocracy to contemporary language.
9th Century Aristocracy in Castile
In the 9th century, the Castilian aristocracy was recognized for their pure lineage, alleged to be untainted by foreign influence. The societal elite in this region of Spain prided themselves on their ancestry, which was thought to be visibly evident in the paleness of their skin and the purportedly blue appearance of their veins. This physical trait was revered and became synonymous with nobility, offering a visible indicator of their social status.
Moors, Nobles, and the ‘Sangre Azul’ Legend
The presence of the Moors in Spain had a significant impact on the society’s perception of nobility. According to legend, old Christian noble families of Castile distinguished themselves from the Moors and other invading populations, boasting that their pure blood had not mixed with the conquerors, dubbing this idea sangre azul, or ‘blue blood’. This legend reflects the deep roots of the term ‘blue blood’, touching on themes of racial purity associated with the medieval nobility of Spain. The aristocracy’s view of themselves as superior due to their ancestry laid the groundwork for the association of ‘blue blood’ with nobility.
Biological and Physiological Explanations
In discussing the association of nobility with the color blue, one must consider the biological and physiological aspects beneath the skin’s surface.
Blue Veins and Pale Skin Phenomena
When observing the skin, especially in individuals with pale complexions, the veins often appear blue. This is not because the blood within them is blue; rather, it’s an optical illusion. Veins look blue due to the way light penetrates the skin and reflects back through the skin’s layers. Light at blue wavelengths is scattered more, and thus, veins can seem blue to the naked eye.
Additionally, in historical contexts, pale skin often indicated a status of nobility, as it suggested a life of leisure indoors, away from manual labor in the sun. The visibility of blue veins in pale skin only accentuated this perception of nobility.
The Science of Blood Coloration
The color of blood is a direct consequence of its composition, primarily the presence of hemoglobin, an iron-rich protein. This protein binds with oxygen, turning the blood a bright red when oxygenated. Conversely, blood that lacks oxygen tends to have a darker red hue but it is never actually blue. In humans, claims of “blue blood” are scientifically inaccurate.
It’s worth mentioning that some creatures do have blue blood. For example, octopuses and some species of crabs use copper, instead of iron, to transport oxygen, resulting in blue blood. However, instances of actual blue skin in humans are the result of rare conditions, such as methemoglobinemia, not a naturally occurring trait linked to oxygen transportation.
Cultural Impact of the Blue Blood Concept

The notion of ‘blue blood’ has long distinguished nobility from commoners, shaping societal structures and perceptions. Its impact resonates through history into modern narratives around class and status.
Nobility as a Separate Class
The term ‘blue blood’ harks back to a time when nobility was seen as a fundamentally separate class, perhaps even akin to another race. This concept cemented the standing of royal families and aristocrats across Europe. In Spain, particularly in the Castile region, the grandees prided themselves on untainted lineage, suggesting that their veins showed blue through pale skin, unlike those who worked outdoors. Noblesse oblige, the idea that nobility extended beyond wealth and included the responsibility of generosity and ethical behavior, also became part of this cultural ethos.
Blue Blood Ideals in Modern Times
Over time, the separation has remained metaphorical, but the attributes associated with “blue blood”—wealth, refinement, and ancestry—persist in how we view modern descendants of noble lines. While the palaces of old may be less central to power, the fascination with royalty and noble descent continues. Magazines and films frequently celebrate the opulence associated with royal families, and social echelons still provide an allure of exclusivity, with wealthy circles often seen as maintaining a figurative moat around their high-status lifestyle.