Ageing of Bruises: Methods and Limitations

When blunt force ruptures small vessels beneath intact skin, blood pools in the subcutaneous or deeper tissues. The colour a bruise shows at any moment reflects where along the haemoglobin degradation pathway the pooled blood currently sits. The pathway is enzymatic and proceeds in one direction.

The direction of travel -- from red-purple to yellow-brown -- is biologically reliable. The timing is not. Classic teaching materials assigned specific age ranges to each colour phase, but peer-reviewed research has consistently failed to validate those ranges with acceptable inter-observer agreement. The 2005 systematic review by Pilling et al., and subsequent work by Maguire and colleagues examining bruising in children, found that colour alone could not reliably distinguish whether a bruise was less than 24 hours old or several days old.

Several biological and environmental variables affect bruise colour and timeline independently of injury age. A forensic nurse must recognise these when examining a patient and note their potential influence in the documentation.

The practical upshot: a bruise's colour at the time of examination is a data point, not a timestamp. The data point is useful for ruling out extreme possibilities (a bright yellow-brown bruise is unlikely to be less than 12 hours old in most adults) but not for assigning a narrow window of hours or a specific day.

Even if a bruise is documented accurately by eye, the photograph that goes into evidence may misrepresent its colour unless specific technical steps are followed. Courts increasingly see expert testimony challenging bruise photographs on colour-accuracy grounds.

1. Include a colour reference card
   Place an X-Rite ColorChecker or similar calibration card in the same frame and lighting as the bruise. This allows the receiving laboratory or court to correct for camera white-balance errors.
2. Use consistent lighting
   Ambient fluorescent light, flash, and natural daylight render skin colour differently. Document the light source used. Where possible, use a standardised clinical photography setup.
3. Add cross-polarised photography for darker skin tones
   Cross-polarised light eliminates surface glare and reveals subsurface pigmentation changes invisible under standard illumination. Equipment: circular polarising filter on lens + polarised flash or ring light.
4. Use alternate-light sources (ALS) where available
   Some forensic units use filtered illumination (typically 415-450 nm wavelength) to enhance bruise contrast. ALS findings are recorded separately from standard photographs and noted in the documentation.
5. Log all metadata
   Record camera settings, time, date, photographer, and case number in the chain-of-custody documentation alongside the image file.

When a forensic nurse or pathologist is asked to give a bruise age in court, the operative question is what the evidence can legitimately support. The answer has two parts, and both matter for professional credibility.

• Defensible: describe the observed colours accurately; state that these colours are consistent with a haemoglobin breakdown stage that is typically associated with a broad time range (e.g., 'days to over a week'); note confounding factors that affect the estimate; and state the limitations explicitly.
• Not defensible: assign a specific date or a narrow age window (e.g., 'this bruise is 48-72 hours old'); state that colour alone proves or disproves a particular history; or fail to acknowledge the documented limitations in the published literature.

The colour of a bruise cannot be used to determine accurately the time of infliction. This applies whether the opinion is given by a nurse, paediatrician, or pathologist.

That conclusion is drawn from a 2005 review by Maguire et al. in the Archives of Disease in Childhood, synthesising available evidence on bruising in children; the same principle applies to adults. Courts that accept more precise testimony are accepting expert opinion that exceeds what the evidence supports. A forensic nurse who testifies accurately about these limits is not weakening their credibility but protecting it.