What Body Fluid Glows Red Under UV Light?
No common body fluid inherently glows red under UV light due to its natural fluorescence. While many body fluids do fluoresce under ultraviolet (UV) light, their typical emissions are not in the red spectrum.
Understanding Body Fluid Fluorescence
Many body fluids contain fluorescent molecules that absorb UV light and then re-emit it at a longer, visible wavelength, causing them to glow. This property is widely utilized by forensic scientists to detect hidden biological evidence at crime scenes. Body fluids such as blood, urine, and semen are known to fluoresce, but they exhibit different colors under UV or "black" light, not typically red.
Typical Fluorescence of Body Fluids Under UV Light
The exact appearance can vary based on factors like the substrate, age of the stain, and specific UV light wavelength, but general observations include:
- Semen: Often appears as a bright bluish-white glow.
- Urine: Typically glows a yellowish-green color.
- Saliva: May exhibit a yellowish glow.
- Blood: Unlike other body fluids, fresh blood stains often appear dark or absorb UV light rather than fluorescing brightly. While UV light is used to locate blood, it's typically through methods that involve specific reagents (like luminol, which produces a blue chemiluminescence) or by observing a lack of fluorescence against a fluorescing background.
Here's a quick overview of common body fluids and their typical UV light responses:
| Body Fluid | Typical UV Response |
|---|---|
| Semen | Bright bluish-white fluorescence |
| Urine | Yellowish-green fluorescence |
| Saliva | Yellowish fluorescence |
| Blood | Absorbs UV light, appearing dark; often detected with reagents |
Addressing the "Red Glow"
While common body fluids do not naturally glow red under UV light, there are specific circumstances or related phenomena that might be confused with this:
- Porphyrins: In rare medical conditions, such as porphyrias, an excess of porphyrins (pigments) can accumulate in the body. When excreted, particularly in urine, these porphyrins can cause the urine to fluoresce red or reddish-brown under long-wave UV light. However, this is due to a medical anomaly, not a general characteristic of urine.
- Forensic Reagents: Some advanced forensic techniques or specific chemical tests designed to identify certain substances might produce a red color or reaction when applied to a body fluid. This reaction is from the chemical interaction, not the inherent fluorescence of the body fluid itself.
In summary, while UV light is a crucial tool for forensic scientists to locate various body fluids due to their fluorescent properties, the characteristic glow is typically in the blue, white, green, or yellow spectrum, not red.
