You finish an SDS-PAGE run and notice that the bands are not level: bands near the edges sit higher, while those in the middle sit lower. This pattern is commonly called “smiling bands.” It can make band positions harder to compare across lanes and raise the question of whether the gel needs to be repeated.

A peer-reviewed review of Western blotting troubleshooting lists several possible contributors to smiling or curved bands, including excessive power, protein overloading, insufficient running buffer, and uneven gel temperature [1]. These are possible causes, not a checklist that proves the source in any one experiment. The appearance should be interpreted alongside the gel, samples, and run conditions.

If your blot also shows weak signal, high background, or unexpected band sizes, consult the broader Western blot troubleshooting guide to compare other common artifacts.

In This Article

  1. What Do Western Blot Smiling Bands Look Like?
  2. Why Do Western Blot Smiling Bands Occur?
  3. How to Fix Western Blot Smiling Bands
  4. A Practical Troubleshooting Workflow
  5. Can Smiling Bands Affect Western Blot Results?
  6. Preventing the Problem in Future Runs
  7. Conclusion
  8. References

1. What Do Western Blot Smiling Bands Look Like?

In a typical smiling pattern, bands near the outer lanes appear higher than bands in the center, producing a curve rather than a straight horizontal line. The shape alone cannot establish the cause. As a practical first check, compare the molecular-weight marker with the sample lanes and determine whether the curvature is shared across much of the gel or limited to particular lanes.

Smiling bands should be distinguished from smearing. Smearing appears as diffuse signal extending along a lane, whereas smiling describes a systematic change in band position across the gel. The two can occur together, but they are not interchangeable.

Observation Initial interpretation First check
Marker and most lanes curve similarly A gel-wide running condition may be involved Review run settings, buffer level, and gel setup
Only a few sample lanes are distorted A sample-specific or local issue is possible Compare sample load, volume, and preparation
Bands are diffuse within lanes Smearing may be the main artifact Review sample integrity and loading conditions
Gel appears straight before transfer but final blot does not The stage causing the appearance is not yet established Compare available records before and after transfer

For an overview of the separation, transfer, and detection stages, see the Western blotting principle and protocol guide.

2. Why Do Western Blot Smiling Bands Occur?

Power settings and uneven temperature

The 2023 review identifies excessive power and a hotter central region of the gel among the reported explanations for smiling bands [1]. This supports checking the electrical running conditions and possible uneven heating, but it does not mean that voltage is always the cause. The review also lists other potential contributors, so a curved pattern should not be attributed to temperature without checking the experimental setup.

Review the settings used for the specific gel and apparatus, including the selected voltage or power mode, run duration, and any signs of unusual warming. Do not apply a universal voltage recommendation across different gel formats and equipment. The appropriate setting depends on the system being used and should follow its validated instructions.

For practical details on running and assembling a gel, consult the Western blot protocol.

Buffer level, gel setup, and sample-related effects

The same review lists insufficient running buffer, detergents or solvents in the sample, and protein overloading among possible explanations for curved migration [1]. These factors should be treated as hypotheses to check, not as causes that can be diagnosed from the curve alone. Confirm the buffer was prepared correctly and that the inner chamber contains enough buffer to cover the wells as required by the apparatus instructions.

When a problem appears limited to particular samples, review the steps in the Western blot sample preparation guide before changing conditions for the entire gel.

Sample overloading is especially worth checking when selected lanes are broad or distorted. Compare the loaded protein amounts and volumes across affected and unaffected lanes. For additional guidance on choosing separation conditions, see the Western blotting optimization guide.

The guide’s section on SDS-PAGE optimization covers gel chemistry and separation conditions.

3. How to Fix Western Blot Smiling Bands

Start with checks that do not require changing the protocol: confirm the running-buffer formulation and level, inspect the gel and apparatus assembly, and review the recorded electrical settings and run duration. If the conditions fall outside the recommendations for the specific system, adjust them according to the gel and equipment instructions. If the buffer preparation is uncertain, prepare it again using the correct formulation.

If a gel defect is suspected, compare the result with a fresh gel prepared or stored correctly. If only selected lanes are affected, review sample amounts, volumes, and preparation before lowering the voltage for the entire run. A protein assay can help establish whether samples were loaded at comparable concentrations.

For the assay options and their sample-compatibility considerations, see protein quantification assay optimization.

Change one factor at a time and compare the next gel with the original. This controlled approach makes the outcome easier to interpret than changing voltage, buffer, sample amount, and cooling simultaneously. The goal is to identify a plausible cause, not simply to make the next gel look better.

4. A Practical Troubleshooting Workflow

First, compare the marker and sample lanes. If most lanes share a similar curve, prioritize conditions affecting the overall run. If the marker looks relatively normal while only a few sample lanes are distorted, examine those samples and their loading conditions first. These are practical troubleshooting heuristics, not definitive rules.

If the gel looked normal immediately after electrophoresis but the final blot image appears distorted, compare the available images and records from each stage. Do not assume that transfer caused the problem solely because the final image looks different. Review the transfer setup and membrane handling as part of the investigation.

For a repeat run, choose the most plausible factor based on the observations and keep the other conditions as consistent as possible. Record the gel type, buffer preparation, electrical settings, run duration, and whether the marker shared the distortion. If the pattern does not improve, reassess the hypothesis rather than changing several additional variables at once.

5. Can Smiling Bands Affect Western Blot Results?

The impact depends on the severity of the distortion and the purpose of the experiment. A mild curve may still allow a target band to be identified, but pronounced curvature can make positions harder to compare across lanes and with the molecular-weight marker. The shape alone does not establish whether a result is valid or invalid.

For quantitative Western blotting, experimental controls, electrophoresis, transfer, detection, imaging, and analysis all contribute to data quality [2]. Smiling bands do not automatically make intensity measurements invalid; the concern is whether the distortion compromises consistent band definition, lane comparison, or interpretation of the target position. If it does, repeating the separation under controlled conditions is preferable to correcting the image by eye.

For a more detailed discussion of normalization and reliable band-intensity measurements, see Boster’s Western blot loading control selection guide.

You can also review the journal article on quantitative Western blot analysis cited below, alongside our How Much Protein Should You Load for Western Blot?.

6. Preventing the Problem in Future Runs

Use the operating conditions recommended for the specific gel and apparatus, prepare the running buffer accurately, and check the gel and tank setup before starting. Keep a record of the settings and the marker’s appearance so that recurring patterns can be compared across runs.

Browse the Western blotting technical resource center for related guides and protocols.

For additional application articles, see the Western blot technical blog archive.

Conclusion

Western blot smiling bands indicate uneven band positions across a gel, but the appearance alone cannot identify the cause. A recent peer-reviewed review lists excessive power, uneven gel temperature, insufficient running buffer, sample-related components, and protein overloading among possible contributors [1]. Start by checking whether the marker and most lanes share the distortion, review the actual running conditions, and test one likely factor at a time.

A mild curve does not automatically invalidate a blot. Repeat the gel when the distortion materially interferes with molecular-weight assignment or the comparisons needed for the experiment.

References

[1] Sule R, Rivera G, Gomes AV. Western blotting (immunoblotting): history, theory, uses, protocol and problems. BioTechniques. 2023;75(3):99–114. doi:10.2144/btn-2022-0034. PubMed

[2] Pillai-Kastoori L, Schutz-Geschwender AR, Harford JA. A systematic approach to quantitative Western blot analysis. Analytical Biochemistry. 2020;593:113608. doi:10.1016/j.ab.2020.113608. PubMed