Posted: Apr 3 2006

Description: A white powdery residue that appears on shells.

It is not a disease! The use of the term “disease” was used before the exact cause was known and it was thought to be caused by bacteria.

What causes it? The white “fluff” are powdery salts (hydrated calcium formates or acetates) resulting from a chemical reaction between the calcium carbonate in the shells and acidic gasses in the air, with water vapor acting as the catalyst. The acidic gasses arise from wood (cabinets and shelves) and any acidic materials used to store or stored with shells (cardboard boxes, cotton, paper, cloth, etc.). Oak is a particularly acidic wood.

Prevention! Essentially there are two steps to prevent Byne’s disease

1. Remove or reduce the presence of sources of acidic gases. Use acid-free materials. Keep storage area well ventilated.

2. Minimize presence of water vapor. Store shells in humidity controlled areas. Be sure shells are thoroughly dry before enclosing in containers such as plastic bags and boxes. Keep storage area well ventilated.

3. Stop it from spreading. Since Byne’s disease is not a disease, but a chemical reaction, it will not “spread.” If it appears, it means conditions are right for the chemical reaction to take place. So, identify the source of the acidic gases or water vapor, remove them, and the chemical reation will stop and the problem will not “spread.” Clean the effected shells (soap and water, maybe some bleach), dry thoroughly and replace in collection. Paul Callomon, Collections Manager Malacology, Invertebrate Paleontology and General Invertebrates, Department of Malacology, Academy of Natural Sciences, Philadelphia, PA noted in Conch-L email on 3/20/09 that, "Bleaches, detergents or solvents are unnecessary (and ineffective) for removing Byne's salts from shells. Just soak the shell in clean water overnight to break up the crystals, then scrub it lightly with a toothbrush under running water and dry it thoroughly."

CLICK HERE for additional discussion of Byne's Disease on the COA website.


The subject of Byne's Disease and prevention was discussed on Conch-L in March 2009.

Mike Schenik asked:

"Anyone know whether a shell sealed in a ziplock bag inside a wood cabinet is at risk for Byne's?"


John Varner replied:

"Technically, polyethylene (ziplock bag material) is slightly permeable to water vapor. Some of the newer versions designed for freezer storage incorporate additives or layered construction to minimize the effects over long storage times. In the food and pharmaceutical packaging industries, this is significant but in this context it is probably negligible. Just be sure the shells are dry when stored."


Charles Sturm, Research Associate - Section of Mollusks Carnegie Museum of Natural History, added:

"Polyethylene is gas permeable. However, it allows for the passage of gasses in a slow fashion. Polyethylene ziplock bags come in 2, 4, 6 mil sizes. The thicker the bag the less the permeability. Thus, using ziplock bags is better than exposing specimens to acidic atmospheric conditions, although maintaining a lower relative humidity and getting rid of things that will give off acids is still the best way to go."


Marien Faber contributed the following comments pointing out another mechanism that can destroy shells - residual sea salt on shells.

"Lots of explanations for Byne's "disease" are available, but what remains unmentioned is perhaps the most common cause: salt (any salt, but usually simply sea salt, NaCl) in combination with microscopic pits and holes on the shell-surface (either natural parts of the microsculpture, or caused by boring sponges, mechanical wear, etc.) and moisture, or, rather cycles of dryness and moisture. What happens is this (I have observed it with the aid of a Scanning Electron Microscope): if there is enough moisture, the salt is in a watery solution and no harm is done. However, when humidity falls, the salt in the pores and crevices will crystalize and by doing so it will simply crush the weaker surrounding calcite matrix of the shell. Repeat this cycle daily (cool nights, warm days), and/or seasonally (moist summer, dry winter) and the shell will disintegrate with an accelerating speed. If you take a close look at old shell collections (for instance the Orbigny type collection in the poorly air-conditioned British Museum) where this process is going on for a considerable time you may notice that spires, and protoconchs go first. And in cypraeids the dorsum goes first. This is logical, since the oldest and most exposed parts of the shells usually are the most damaged, on a microscopic level, by mechanical wear and boring and etching organisms.

What to do? Simple: wash ALL shells (even land and so-called "fresh water" shells) thoroughly in distilled water and store them under even moisture and temperature conditions."

Upon reading Marien's comments,
John Varner elaborated with "a bit more on salt & saline solutions:"

"At a relative humidity of about 75% (at which point the air feels "sticky", but below what is common in the Southeastern US, or anywhere close to a body of water, especially in the evenings as the temperature drops) a saturated salt (NaCl) solution will pick up water vapor from the air. (Different salts have different RHs for this phenomenon, which can be exploited to create precise RHs in enclosed spaces, allowing for the calibration of hygrometers) As the RH drops below 75%, the solution will give up water vapor to the air at the interface between the solution and air until it is once again saturated, and salt will then begin to crystallize out of solution until all the water is evaporated or the ambient air is @ 75% RH. That is to say that if the RH fluctuates around 75%, the situation Marien describes below will become a big problem. If the RH stays below 75%, it is less of an issue. However, one must bear in mind that even a few degrees fluctuation in temperature results in a dramatic change in RH - warm air holds much more water vapor than cool air - so if a collection is stored in an area with temperature fluctuations, the RH will also fluctuate, possibly leading to cycles of condensation & evaporation. This is why basements tend to be damp & prone to mildew - if the air outside is 80 degrees and the RH is 60%, by the time it enters a basement at 65 degrees, the RH starts approaching the dew point (100% RH). I.e.: if a collection is stored in a basement, use a dehumidifier."