Study finds biofilm on externally threaded body jewelry

TopicsInternal + External | Needles + Catheters

A study published by the Journal of Adolescent Health has been inaccurately reported to claim that plastic jewelry is safer than metal for tongue piercings because of the greater biofilm found when jewelry is extracted after two weeks in place.

The basic premise of their conclusion is sound:

“The low bacterial counts from piercing channels suggest that having a tongue pierced would not contribute to an increased risk for oral infection.”

However, we can draw significantly different conclusions from the findings of this study:

  1. Externally threaded* metal jewelry does not seal as well as the same design in plastic.
  2. This study suggests that bacteria is introduced to inside of the piercing when externally threaded jewelry is removed.
  3. We now need results of a similar study repeated with only jewelry that has tightly sealed internally threaded posts with highly polished surfaces that are fully cleaned and passivated before sterilization to eliminate bias and more effectively test the hypothesis of materials.
Externally threaded compared with internally threaded body jewelry thanks to Brian McRorie Joel Burgess from Planet Three Piercing
Externally threaded compared with internally threaded body jewelry thanks to Brian McRorie Joel Burgess from Planet Three Piercing

A few important factors to note:

This study was done with externally threaded posts of an unspecified material and surface finish quality. The bacteria found in the piercing channel was measured after a colonized exposed screw thread was pulled through the piercing, leaving debris behind. Researchers should swab the area before removing the ball ends, and swab both sections of the threads as well before removing the jewelry.

External threads for body jewelry rarely seal, and can shed particulates.

Hardened plaque deposits and biofilm can be found at the closure of a piece of oral body jewelry. This appears in comparatively significant smaller quantities when the surface finish of the jewelry is smoother, and the closure of the jewelry is well sealed. This issue is well observed by experienced body piercing professionals.

Externally threaded plastic posts sometimes have a tighter tolerance at the closure than their metal counterparts, and a better seal means less bacterial colonization. This alone does not demonstrate that plastic as a better body jewelry material than metal, instead in this context it indicates strongly that the quality of the closure is of importance, without regard to the material.

The study does not mention the manufacturer of the jewelry used, nor the surface finishing and passivation processes. It does not specify ASTM F86 standards for were followed or the specific surface roughness Ra, only that PTFE was the roughest surface they used.

The surface finish and the quality of the mechanical closure of the jewelry makes a huge difference in biofilm formation. Differences in surface roughness between the materials was mentioned, but not quantified.

PTFE jewelry surface defects
An example of why plastic jewelry can be problematic

Because the standards for what is considered safe enough for body jewelry have been debated  in the piercing community for many years. The Association of Professional Piercers has agreed upon minimum standards for body jewelry specified here: details some of the further issues involved to clarify body jewelry quality and safety standards.

Internal vs. External Threading

More information related to the article in The Point! 57 page 10 “Step-down threading”

The Point! 57

Look for the following qualities in well manufactured Internal or External jewelry:

  • Free of nicks and burrs, no polishing compounds, threads well cleaned
  • Use of appropriate metals.  Mill Specifications and MSDS / ISO sheets available from manufacturer that certify ASTM F138 Steel for surgical implant or ASTM F136 or F67 Titanium for surgical implant. Current APP jewelry standards here:

Look for the following qualities in poorly manufactured Internal or External jewelry:

  • Burrs
  • Tooling marks
  • Not enough or too much threading (exposed screw threads when closed)

Look for the following qualities in well manufactured Internal jewelry:

  • Smooth round ends.
  • Universal threading standard (1.2mm on 14 and 12 gauge, .080 on 10 gauge)
  • Ball screws all the way down, no gaps or cavities at the connection
  • Posts should be solid.
  • Often a good manufacturer of internal will have better quality control throughout the range but this is not always the case.

Look for the following qualities in poorly manufactured Internal jewelry:

  • Flat cut ends and/or hollow posts.
  • If the ball is not countersunk there will be a gap to collect waste possibly irritate the piercing. Poorly fitted balls allow waste to collect in the counter sinking of the ball. Even the best internally threaded jewelry will leave a small gap where a countersunk ball fits over the post.
  • Sharp edges, threaded insert falling out, inserts made from other than implant materials.
  • More expensive to make, passed on to client, less competitive.
  • Higher degree of technical skill is required for a smooth jewelry transfer. Use of guide wire “snips” or pin-coupling / cuplink tapers facilitates an easier transfer, reducing lost connections.

Procedural Application of well manufactured Internal jewelry:

  • Can be used with Piercing needle or Cannula methods.
  • Is appropriate in new, newly healed or well healed piercing.

Look for the following qualities in well manufactured External jewelry:

  • Threads may be easier to clean than internal, (holds less polishing compound).
  • The end of the thread is rounded.
  • There is less problem with inserting external in a well healed and seasoned piercing, providing the person has experience with the jewelry.
  • Obviously tapers are often needed with either style of jewelry.
  • The vast majority of piercers are using externally threaded jewelry without complications.
  • Countersinking of the ball is not an issue as the ball should fit over the stem completely and lock tight.
  • Less costly than internally threaded.
  • More readily available in a wider variety of designs.
  • There isn’t always, but there tends to be greater inconsistencies in quality even sometimes within the same manufacturer’s range.

Look for the following qualities in poorly manufactured External jewelry:

  • Possible problem of very small step-down thread design that fits into the piercing needle, vulnerable to snapping off inside the needle.
  • Poorly fitted balls will allow for collection of waste in the hollow ball.
  • Insufficient number of threads. Threads or ball can strip.

Procedural Application of well manufactured External jewelry:

  • Mixed reviews on use with piercing needles.
  • Many piercers express they can feel the jewelry snagging during the jewelry transfer.
  • Frequently this is felt by the client.
  • Step-down external threaded jewelry seems to minimize this.
  • Acceptable for use with Cannula style of Piercing.
  • Many practitioners find it easier to perform the jewelry transfer with a Cannula.
  • Some shops that pierce with internal will use external in well-healed piercings.

Piercing Needles and Cannula (Catheters, Introcan, etc):

  • Like with internal and external there are good piercings needles and bad, good cannula and bad.

Piercing Needle-

A quality piercing needle by Industrial Strength LLC


  • Less bleeding than when using cannula.


  • Harder to do jewelry transfers without a connection pin or tapered guide than cannula, possibility for a greater percentage of transfer failure.


Introcan cannula by Braun


  • Sharper than low quality piercing needles.
  • Easier jewelry transfer.
  • Pre-sterilized, hospital grade, gamma-radiation, more readily available than piercing needles.
  • Gamma-radiation sterilization is the preferred method for sterilization of single-use items for many in the medical field. An advantage over autoclaving is that no spore test is needed.


  • In extremely rare cases the plastic sleeve collapses.
  • Sleeve can be rough if cut.
  • Increased bleeding in some piercings, as compared to piercing needles because the sleeve is slightly larger than than the jewelry.
  • Adds time to the piercing process waiting for the tissue to contract and for the bleeding to coagulate.
  • To avoid bleeding some piercers have used smaller cannula size than the jewelry, this creates a tight fit in the sleeve making the jewelry transfer a slight stretch and less smooth.
  • More expensive than piercing needles.

From the Association of Professional Piercers educational presentation materials

2 thoughts on “Study finds biofilm on externally threaded body jewelry”

  1. Very informative article, this research is really helpful for all those who are planning to have a tongue piercing. We should be very cautious of choosing the right jewelry before proceeding to the procedure, we can also the professional some questions if new to piercing, in this way we will be more educated and will know what is best for us.


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